[Driver][ARM] Warn about -mabi= for assembler input with -fno-integrated-as

[MaskRay]

Summary

Similar to D153691, but for -x assembler -fno-integrated-as.

Close https://github.com/ClangBuiltLinux/linux/issues/1878

[michaelplatings]

LGTM

clang/lib/Driver/ToolChains/Gnu.cpp

case arm::FloatABI::Hard:
       CmdArgs.push_back(Args.MakeArgString("-mfloat-abi=hard"));
       break;
     }
 
     Args.AddLastArg(CmdArgs, options::OPT_march_EQ);
     normalizeCPUNamesForAssembler(Args, CmdArgs);
 
     Args.AddLastArg(CmdArgs, options::OPT_mfpu_EQ);
+    // The integrated assembler doesn't implement e_flags setting behavior for
+    // -meabi=gnu (gcc -mabi={apcs-gnu,atpcs} passes -meabi=gnu to gas). For
+    // compatibility we accept but warn.
+    if (Arg *A = Args.getLastArgNoClaim(options::OPT_mabi_EQ))
+      A->ignoreTargetSpecific();
     break;
   }
   case llvm::Triple::aarch64:
   case llvm::Triple::aarch64_be: {
     CmdArgs.push_back(
         getToolChain().getArch() == llvm::Triple::aarch64_be ? "-EB" : "-EL");
     Args.AddLastArg(CmdArgs, options::OPT_march_EQ);
     normalizeCPUNamesForAssembler(Args, CmdArgs);

clang/test/Driver/arm-abi.c

 // RUN:   | FileCheck -check-prefix=CHECK-AAPCS-LINUX %s
 
 // CHECK-APCS-GNU: "-target-abi" "apcs-gnu"
 // CHECK-AAPCS: "-target-abi" "aapcs"
 // CHECK-AAPCS-LINUX: "-target-abi" "aapcs-linux"
 
 // RUN: %clang --target=arm---gnueabi -mabi=aapcs -x assembler %s -### -o /dev/null 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-ASM %s
+// RUN: %clang --target=arm---gnueabi -mabi=aapcs -x assembler %s -### -o /dev/null -fno-integrated-as 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-ASM %s
 
 /// The combination -x assember & -mabi is not implemented, but for GCC compatibility we accept with a warning.
 // CHECK-ASM: warning: argument unused during compilation: '-mabi={{.*}}'

clang/test/Driver/linux-as.c

 // RUN:   | FileCheck -check-prefix=CHECK-ARM-MCPU %s
 // CHECK-ARM-MCPU: as{{(.exe)?}}" "-EL" "-mfloat-abi=soft" "-mcpu=cortex-a8"
 //
 // RUN: %clang -target arm-linux -mfpu=neon -### \
 // RUN:   -no-integrated-as -c %s 2>&1 \
 // RUN:   | FileCheck -check-prefix=CHECK-ARM-MFPU %s
 // CHECK-ARM-MFPU: as{{(.exe)?}}" "-EL" "-mfloat-abi=soft" "-mfpu=neon"
 //
-// RUN: %clang -target arm-linux -march=armv7-a -### \
+// RUN: %clang --target=arm-linux -march=armv7-a -mabi=aapcs-linux -### \
 // RUN:   -no-integrated-as -c %s 2>&1 \
 // RUN:   | FileCheck -check-prefix=CHECK-ARM-MARCH %s
 // CHECK-ARM-MARCH: as{{(.exe)?}}" "-EL" "-mfloat-abi=soft" "-march=armv7-a"
+// CHECK-ARM-MARCH-NOT: "-mabi=
 //
 // RUN: %clang -target armeb-linux -mlittle-endian -mcpu=cortex-a8 -mfpu=neon -march=armv7-a -### \
 // RUN:   -no-integrated-as -c %s 2>&1 \
 // RUN:   | FileCheck -check-prefix=CHECK-ARM-ALL %s
 // CHECK-ARM-ALL: as{{(.exe)?}}" "-EL" "-mfloat-abi=soft" "-march=armv7-a" "-mcpu=cortex-a8" "-mfpu=neon"
 //
 // RUN: %clang -target arm-linux -mcpu=cortex-a8 -mfpu=neon -march=armv7-a -### \
 // RUN:   -no-integrated-as -c %s 2>&1 \