Fix handling of reserved registers for ARM inline asm

[Amanieu]

r6 is now disallowed as an operand since LLVM sometimes uses it as a base pointer.

The check against using the frame pointer as an operand now takes the platform into account and will block either r7 or r11 as appropriate.

Fixes #73450

cc @cbiffle

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##[section]Starting: Linux mingw-check
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---
 ---> a9ec21d337b3
Step 6/7 : ENV RUN_CHECK_WITH_PARALLEL_QUERIES 1
 ---> Using cache
 ---> 5ff2c13d8dba
Step 7/7 : ENV SCRIPT python3 ../x.py test src/tools/expand-yaml-anchors &&            python3 ../x.py check --target=i686-pc-windows-gnu --host=i686-pc-windows-gnu &&            python3 ../x.py build --stage 0 src/tools/build-manifest &&            python3 ../x.py test --stage 0 src/tools/compiletest &&            python3 ../x.py test src/tools/tidy &&            python3 ../x.py doc --stage 0 src/libstd &&            /scripts/validate-toolstate.sh
 ---> 6b931e755c7e
Successfully built 6b931e755c7e
Successfully tagged rust-ci:latest
Built container sha256:6b931e755c7ea1f69816640eb9df74fafd40a545d0e5aa8341d35009dabb0f3c
---
error[E0061]: this function takes 4 arguments but 3 arguments were supplied
   --> src/librustc_target/asm/mod.rs:263:31
    |
84  | /             pub fn parse(
85  | |                 _arch: super::InlineAsmArch,
86  | |                 mut _has_feature: impl FnMut(&str) -> bool,
87  | |                 _target: &crate::spec::Target,
101 | |                 }
102 | |             }
    | |_____________- defined here
...
...
263 |                   Self::Hexagon(HexagonInlineAsmReg::parse(arch, has_feature, &name)?)
    |                                 |
    |                                 expected 4 arguments

error[E0061]: this function takes 4 arguments but 3 arguments were supplied
error[E0061]: this function takes 4 arguments but 3 arguments were supplied
   --> src/librustc_target/asm/mod.rs:575:13
    |
105 | /         pub(super) fn fill_reg_map(
106 | |             _arch: super::InlineAsmArch,
107 | |             mut _has_feature: impl FnMut(&str) -> bool,
108 | |             _target: &crate::spec::Target,
127 | |             )*
128 | |         }
    | |_________- defined here
...
...
575 |               hexagon::fill_reg_map(arch, has_feature, &mut map);
    |               |
    |               expected 4 arguments

error: aborting due to 2 previous errors
error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0061`.
error: could not compile `rustc_target`.

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failed to run: /checkout/obj/build/bootstrap/debug/bootstrap check
Build completed unsuccessfully in 0:03:34
== clock drift check ==
  local time: Sun Jun 21 17:53:56 UTC 2020
  local time: Sun Jun 21 17:53:56 UTC 2020
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== end clock drift check ==

##[error]Bash exited with code '1'.
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 ---> Using cache
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Step 7/7 : ENV SCRIPT python3 ../x.py test src/tools/expand-yaml-anchors &&            python3 ../x.py check --target=i686-pc-windows-gnu --host=i686-pc-windows-gnu &&            python3 ../x.py build --stage 0 src/tools/build-manifest &&            python3 ../x.py test --stage 0 src/tools/compiletest &&            python3 ../x.py test src/tools/tidy &&            python3 ../x.py doc --stage 0 src/libstd &&            /scripts/validate-toolstate.sh
 ---> 6b931e755c7e
Successfully built 6b931e755c7e
Successfully tagged rust-ci:latest
Built container sha256:6b931e755c7ea1f69816640eb9df74fafd40a545d0e5aa8341d35009dabb0f3c
---
error[E0061]: this function takes 4 arguments but 3 arguments were supplied
   --> src/librustc_target/asm/mod.rs:263:31
    |
84  | /             pub fn parse(
85  | |                 _arch: super::InlineAsmArch,
86  | |                 mut _has_feature: impl FnMut(&str) -> bool,
87  | |                 _target: &crate::spec::Target,
101 | |                 }
102 | |             }
    | |_____________- defined here
...
...
263 |                   Self::Hexagon(HexagonInlineAsmReg::parse(arch, has_feature, &name)?)
    |                                 |
    |                                 expected 4 arguments

error: aborting due to previous error
error: aborting due to previous error

For more information about this error, try `rustc --explain E0061`.
error: could not compile `rustc_target`.

To learn more, run the command again with --verbose.
warning: build failed, waiting for other jobs to finish...
error: build failed
command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "check" "--target" "x86_64-unknown-linux-gnu" "-Zbinary-dep-depinfo" "-j" "2" "--release" "--color" "always" "--features" " llvm" "--manifest-path" "/checkout/src/rustc/Cargo.toml" "--message-format" "json-render-diagnostics"
failed to run: /checkout/obj/build/bootstrap/debug/bootstrap check
Build completed unsuccessfully in 0:04:06
== clock drift check ==
  local time: Sun Jun 21 18:05:57 UTC 2020
  local time: Sun Jun 21 18:05:57 UTC 2020
  network time: Sun, 21 Jun 2020 18:05:57 GMT
== end clock drift check ==

##[error]Bash exited with code '1'.
##[section]Finishing: Run build
##[section]Starting: Checkout rust-lang/rust@refs/pull/73588/merge to s
Task         : Get sources
Description  : Get sources from a repository. Supports Git, TfsVC, and SVN repositories.
Version      : 1.0.0
Author       : Microsoft
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Help         : [More Information](https://go.microsoft.com/fwlink/?LinkId=798199)
==============================================================================
Cleaning any cached credential from repository: rust-lang/rust (GitHub)
##[section]Finishing: Checkout rust-lang/rust@refs/pull/73588/merge to s
Cleaning up task key
Start cleaning up orphan processes.
Terminate orphan process: pid (3560) (python)
##[section]Finishing: Finalize Job

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[nagisa]

@bors r+

[bors]

📌 Commit be52cfa8d58d61972876a91e8328cdac6a58cf4f has been approved by nagisa

[Amanieu]

@bors r=nagisa

[bors]

📌 Commit a98868d has been approved by nagisa