Use only installed Python on Windows

When Python is installed on Windows separately (i.e. Windows Store,
Python.org MSI, etc.) it set the PYTHONHOME environment variable to
the installed path.

When we call our own portable Python, it tries to use the support
PYC files in PYTHONHOME.  If they're from a different version of
Python, however, they won't work.  Even though we're running our
own distributed Python.exe, we are crashing on the system-wide
Python installation.

Add -I to all python3 calls, ignore PYTHONHOME/etc. environment vars.

Tested under Ubuntu 18.04 Linux w/o any ill effects (we ship pyserial
ourselves and add it manually to the Python search path).

Fixes #8096, or should as I understand it.

platform.txt

@@ -96,13 +96,13 @@ compiler.elf2hex.extra_flags=
 
 ## generate file with git version number
 ## needs git
-recipe.hooks.sketch.prebuild.pattern="{runtime.tools.python3.path}/python3" "{runtime.tools.signing}" --mode header --publickey "{build.source.path}/public.key" --out "{build.path}/core/Updater_Signing.h"
+recipe.hooks.sketch.prebuild.pattern="{runtime.tools.python3.path}/python3" -I "{runtime.tools.signing}" --mode header --publickey "{build.source.path}/public.key" --out "{build.path}/core/Updater_Signing.h"
 # This is quite a working hack. This form of prebuild hook, while intuitive, is not explicitly documented.
-recipe.hooks.prebuild.pattern="{runtime.tools.python3.path}/python3" "{runtime.tools.makecorever}" --build_path "{build.path}" --platform_path "{runtime.platform.path}" --version "{version}"
+recipe.hooks.prebuild.pattern="{runtime.tools.python3.path}/python3" -I "{runtime.tools.makecorever}" --build_path "{build.path}" --platform_path "{runtime.platform.path}" --version "{version}"
 
 ## Build the app.ld linker file
-recipe.hooks.linking.prelink.1.pattern="{runtime.tools.python3.path}/python3" "{runtime.tools.mkdir}" -p "{build.path}/ld_h/"
-recipe.hooks.linking.prelink.2.pattern="{runtime.tools.python3.path}/python3" "{runtime.tools.cp}" "{runtime.platform.path}/tools/sdk/ld/{build.flash_ld}" "{build.path}/ld_h/local.eagle.flash.ld.h"
+recipe.hooks.linking.prelink.1.pattern="{runtime.tools.python3.path}/python3" -I "{runtime.tools.mkdir}" -p "{build.path}/ld_h/"
+recipe.hooks.linking.prelink.2.pattern="{runtime.tools.python3.path}/python3" -I "{runtime.tools.cp}" "{runtime.platform.path}/tools/sdk/ld/{build.flash_ld}" "{build.path}/ld_h/local.eagle.flash.ld.h"
 recipe.hooks.linking.prelink.3.pattern="{compiler.path}{compiler.c.cmd}" -CC -E -P {build.vtable_flags} {build.mmuflags} "{build.path}/ld_h/local.eagle.flash.ld.h" -o "{build.path}/local.eagle.flash.ld"
 recipe.hooks.linking.prelink.4.pattern="{compiler.path}{compiler.c.cmd}" -CC -E -P {build.vtable_flags} {build.mmuflags} "{runtime.platform.path}/tools/sdk/ld/eagle.app.v6.common.ld.h" -o "{build.path}/local.eagle.app.v6.common.ld"
 
@@ -125,9 +125,9 @@ recipe.c.combine.pattern="{compiler.path}{compiler.c.elf.cmd}" {build.exception_
 recipe.objcopy.eep.pattern=
 
 ## Create hex
-recipe.objcopy.hex.1.pattern="{runtime.tools.python3.path}/python3" "{runtime.tools.elf2bin}" --eboot "{runtime.tools.eboot}" --app "{build.path}/{build.project_name}.elf" --flash_mode {build.flash_mode} --flash_freq {build.flash_freq} --flash_size {build.flash_size} --path "{runtime.tools.xtensa-lx106-elf-gcc.path}/bin" --out "{build.path}/{build.project_name}.bin"
-recipe.objcopy.hex.2.pattern="{runtime.tools.python3.path}/python3" "{runtime.tools.signing}" --mode sign --privatekey "{build.source.path}/private.key" --bin "{build.path}/{build.project_name}.bin" --out "{build.path}/{build.project_name}.bin.signed" --legacy "{build.path}/{build.project_name}.bin.legacy_sig"
-recipe.objcopy.hex.3.pattern="{runtime.tools.python3.path}/python3" "{runtime.tools.sizes}" --elf "{build.path}/{build.project_name}.elf" --path "{runtime.tools.xtensa-lx106-elf-gcc.path}/bin" --mmu "{build.mmuflags}"
+recipe.objcopy.hex.1.pattern="{runtime.tools.python3.path}/python3" -I "{runtime.tools.elf2bin}" --eboot "{runtime.tools.eboot}" --app "{build.path}/{build.project_name}.elf" --flash_mode {build.flash_mode} --flash_freq {build.flash_freq} --flash_size {build.flash_size} --path "{runtime.tools.xtensa-lx106-elf-gcc.path}/bin" --out "{build.path}/{build.project_name}.bin"
+recipe.objcopy.hex.2.pattern="{runtime.tools.python3.path}/python3" -I "{runtime.tools.signing}" --mode sign --privatekey "{build.source.path}/private.key" --bin "{build.path}/{build.project_name}.bin" --out "{build.path}/{build.project_name}.bin.signed" --legacy "{build.path}/{build.project_name}.bin.legacy_sig"
+recipe.objcopy.hex.3.pattern="{runtime.tools.python3.path}/python3" -I "{runtime.tools.sizes}" --elf "{build.path}/{build.project_name}.elf" --path "{runtime.tools.xtensa-lx106-elf-gcc.path}/bin" --mmu "{build.mmuflags}"
 
 ## Save hex
 recipe.output.tmp_file={build.project_name}.bin
@@ -158,9 +158,8 @@ tools.esptool.upload.params.quiet=
 # First, potentially perform an erase or nothing
 # Next, do the binary upload
 # Combined in one rule because Arduino doesn't support upload.1.pattern/upload.3.pattern
-tools.esptool.upload.pattern="{cmd}" "{runtime.platform.path}/tools/upload.py" --chip esp8266 --port "{serial.port}" --baud "{upload.speed}" "{upload.verbose}" {upload.erase_cmd} {upload.resetmethod} write_flash 0x0 "{build.path}/{build.project_name}.bin"
-
-tools.esptool.upload.network_pattern="{network_cmd}" "{runtime.platform.path}/tools/espota.py" -i "{serial.port}" -p "{network.port}" "--auth={network.password}" -f "{build.path}/{build.project_name}.bin"
+tools.esptool.upload.pattern="{cmd}" -I "{runtime.platform.path}/tools/upload.py" --chip esp8266 --port "{serial.port}" --baud "{upload.speed}" "{upload.verbose}" {upload.erase_cmd} {upload.resetmethod} write_flash 0x0 "{build.path}/{build.project_name}.bin"
+tools.esptool.upload.network_pattern="{network_cmd}" -I "{runtime.platform.path}/tools/espota.py" -i "{serial.port}" -p "{network.port}" "--auth={network.password}" -f "{build.path}/{build.project_name}.bin"
 
 tools.mkspiffs.cmd=mkspiffs
 tools.mkspiffs.cmd.windows=mkspiffs.exe