testsuite: Skip tests incompatible with generic thunk support

Some backends do not define TARGET_ASM_OUTPUT_MI_THUNK.  But the generic
thunk support cannot emit code for calling variadic methods of
multiple-inheritance classes.  Example error for pru-unknown-elf:

 .../gcc/gcc/testsuite/g++.dg/ipa/pr83549.C:7:24: error: generic thunk code fails for method 'virtual void C::_ZThn4_N1C3fooEz(...)' which uses '...'

Disable the affected tests for all targets which do not define
TARGET_ASM_OUTPUT_MI_THUNK.

Ensured that test results with and without this patch for
x86_64-pc-linux-gnu are the same.

gcc/ChangeLog:

	* doc/sourcebuild.texi: Document variadic_mi_thunk effective
	target check.

gcc/testsuite/ChangeLog:

	* g++.dg/ipa/pr83549.C: Require effective target
	variadic_mi_thunk.
	* g++.dg/ipa/pr83667.C: Ditto.
	* g++.dg/torture/pr81812.C: Ditto.
	* g++.old-deja/g++.jason/thunk3.C: Ditto.
	* lib/target-supports.exp
	(check_effective_target_variadic_mi_thunk): New function.

Signed-off-by: Dimitar Dimitrov <dimitar@dinux.eu>

Author: Dimitar Dimitrov

gcc/doc/sourcebuild.texi

@@ -2957,6 +2957,9 @@ Target supports @code{sysconf}.
 @item trampolines
 Target supports trampolines.
 
+@item variadic_mi_thunk
+Target supports C++ virtual variadic function calls with multiple inheritance.
+
 @item two_plus_gigs
 Target supports linking programs with 2+GiB of data.
 

gcc/testsuite/g++.dg/ipa/pr83549.C

@@ -1,5 +1,6 @@
 // PR ipa/83549
 // { dg-do compile }
+// { dg-require-effective-target variadic_mi_thunk }
 // { dg-options "-O2" }
 
 struct A { virtual ~A (); };

gcc/testsuite/g++.dg/ipa/pr83667.C

@@ -1,6 +1,7 @@
 // { dg-require-alias "" }
 // { dg-options "-fdump-ipa-inline" }
 // c++/83667 ICE dumping a static thunk when TARGET_USE_LOCAL_THUNK_ALIAS_P
+// { dg-require-effective-target variadic_mi_thunk }
 
 
 struct a

gcc/testsuite/g++.dg/torture/pr81812.C

@@ -1,4 +1,5 @@
 // { dg-xfail-if "PR108277" { arm_thumb1 } }
+// { dg-require-effective-target variadic_mi_thunk }
 
 struct Error {
   virtual void error(... ) const;

gcc/testsuite/g++.old-deja/g++.jason/thunk3.C

@@ -1,5 +1,6 @@
 // { dg-do run }
-// { dg-skip-if "fails with generic thunk support" { rs6000-*-* powerpc-*-eabi v850-*-* sh-*-* h8*-*-* xtensa*-*-* m32r*-*-* lm32-*-* } }
+// { dg-skip-if "fails with generic thunk support" { rs6000-*-* powerpc-*-eabi sh-*-* xtensa*-*-* } }
+// { dg-require-effective-target variadic_mi_thunk }
 // Test that variadic function calls using thunks work right.
 // Note that this will break on any target that uses the generic thunk
 //  support, because it doesn't support variadic functions.

gcc/testsuite/lib/target-supports.exp

@@ -659,6 +659,37 @@ proc check_effective_target_trampolines { } {
     return 1
 }
 
+# Return 1 if target supports calling virtual variadic methods
+# of multi-inheritance classes.
+
+proc check_effective_target_variadic_mi_thunk { } {
+    # These targets do not implement TARGET_ASM_OUTPUT_MI_THUNK.
+    if { [istarget avr-*-*]
+	 || [istarget bpf-*-*]
+	 || [istarget fr30-*-*]
+	 || [istarget ft32-*-*]
+	 || [istarget amdgcn-*-*]
+	 || [istarget h8300-*-*]
+	 || [istarget iq2000-*-*]
+	 || [istarget lm32-*-*]
+	 || [istarget m32c-*-*]
+	 || [istarget m32r-*-*]
+	 || [istarget mcore-*-*]
+	 || [istarget moxie-*-*]
+	 || [istarget msp430-*-*]
+	 || [istarget nvptx-*-*]
+	 || [istarget pdp11-*-*]
+	 || [istarget pru-*-*]
+	 || [istarget rl78-*-*]
+	 || [istarget rx-*-*]
+	 || [istarget v850-*-*]
+	 || [istarget visium-*-*] } {
+
+	return 0;
+    }
+    return 1
+}
+
 # Return 1 if target has limited stack size.
 
 proc check_effective_target_stack_size { } {