clang: Always pass PowerPC endian information to GNU as

When building a 64-bit big endian PowerPC Linux kernel with a 64-bit
little endian PowerPC target, the 32-bit vDSO errors:

```
$ make ARCH=powerpc CC=clang CROSS_COMPILE=powerpc64le-linux-gnu- \
       pseries_defconfig arch/powerpc/kernel/vdso32/
ld.lld: error: arch/powerpc/kernel/vdso32/sigtramp.o is incompatible with elf32-powerpc
ld.lld: error: arch/powerpc/kernel/vdso32/gettimeofday.o is incompatible with elf32-powerpc
ld.lld: error: arch/powerpc/kernel/vdso32/datapage.o is incompatible with elf32-powerpc
ld.lld: error: arch/powerpc/kernel/vdso32/cacheflush.o is incompatible with elf32-powerpc
ld.lld: error: arch/powerpc/kernel/vdso32/note.o is incompatible with elf32-powerpc
ld.lld: error: arch/powerpc/kernel/vdso32/getcpu.o is incompatible with elf32-powerpc
ld.lld: error: arch/powerpc/kernel/vdso32/vgettimeofday.o is incompatible with elf32-powerpc
...
```

This happens because the endian information is missing from the call to
the assembler, even though it was explicitly passed to clang. See the
below example.

```
$ echo | clang --target=powerpc64le-linux-gnu \
               --prefix=/usr/bin/powerpc64le-linux-gnu- \
               -no-integrated-as -m32 -mbig-endian -### -x c -c -
 ".../clang-12" "-cc1" "-triple" "powerpc-unknown-linux-gnu" ...
...
  "/usr/bin/powerpc64le-linux-gnu-as" "-a32" "-mppc" "-many" "-o" "-.o" "/tmp/--e69e28.s"
```

clang sets the right target with -m32 and -mbig-endian but -mbig-endian
does not make it to the assembler, resulting in a 32-bit little endian
binary. This differs from the little endian targets, which always pass
-mlittle-endian.

```
$ echo | clang --target=powerpc64-linux-gnu \
               --prefix=/usr/bin/powerpc64-linux-gnu- \
               -no-integrated-as -m32 -mlittle-endian -### -x c -c -
 ".../clang-12" "-cc1" "-triple" "powerpcle-unknown-linux-gnu" ...
...
 "/usr/bin/powerpc64-linux-gnu-as" "-a32" "-mppc" "-mlittle-endian" "-many" "-o" "-.o" "/tmp/--405dbd.s"
```

Do the same thing for the big endian targets so that there is no more
error. This matches GCC's behavior, where -mbig and -mlittle are always
passed along to GNU as.

```
$ echo | powerpc64-linux-gcc -### -x c -c -
...
.../powerpc64-linux/bin/as -a64 -mpower4 -many -mbig -o -.o /tmp/ccVn7NAm.s
...

$ echo | powerpc64le-linux-gcc -### -x c -c -
...
.../powerpc64le-linux/bin/as -a64 -mpower8 -many -mlittle -o -.o /tmp/ccPN9ato.s
...
```

Reviewed By: nickdesaulniers, MaskRay

Differential Revision: https://reviews.llvm.org/D94442

clang/lib/Driver/ToolChains/Gnu.cpp

@@ -731,6 +731,7 @@ void tools::gnutools::Assembler::ConstructJob(Compilation &C,
   case llvm::Triple::ppc: {
     CmdArgs.push_back("-a32");
     CmdArgs.push_back("-mppc");
+    CmdArgs.push_back("-mbig-endian");
     CmdArgs.push_back(
       ppc::getPPCAsmModeForCPU(getCPUName(Args, getToolChain().getTriple())));
     break;
@@ -746,6 +747,7 @@ void tools::gnutools::Assembler::ConstructJob(Compilation &C,
   case llvm::Triple::ppc64: {
     CmdArgs.push_back("-a64");
     CmdArgs.push_back("-mppc64");
+    CmdArgs.push_back("-mbig-endian");
     CmdArgs.push_back(
       ppc::getPPCAsmModeForCPU(getCPUName(Args, getToolChain().getTriple())));
     break;

clang/test/Driver/ppc-features.cpp

@@ -156,14 +156,25 @@
 // CHECK-NOSPE: "-target-feature" "-spe"
 
 // Assembler features
-// RUN: %clang -target powerpc64-unknown-linux-gnu %s -### -o %t.o -no-integrated-as 2>&1 | FileCheck -check-prefix=CHECK_BE_AS_ARGS %s
-// CHECK_BE_AS_ARGS: "-mppc64"
-// CHECK_BE_AS_ARGS: "-many"
+// RUN: %clang -target powerpc-unknown-linux-gnu %s -### -o %t.o -no-integrated-as 2>&1 | FileCheck -check-prefix=CHECK_32_BE_AS_ARGS %s
+// CHECK_32_BE_AS_ARGS: "-mppc"
+// CHECK_32_BE_AS_ARGS-SAME: "-mbig-endian"
+// CHECK_32_BE_AS_ARGS-SAME: "-many"
 
-// RUN: %clang -target powerpc64le-unknown-linux-gnu %s -### -o %t.o -no-integrated-as 2>&1 | FileCheck -check-prefix=CHECK_LE_AS_ARGS %s
-// CHECK_LE_AS_ARGS: "-mppc64"
-// CHECK_LE_AS_ARGS: "-mlittle-endian"
-// CHECK_LE_AS_ARGS: "-mpower8"
+// RUN: %clang -target powerpcle-unknown-linux-gnu %s -### -o %t.o -no-integrated-as 2>&1 | FileCheck -check-prefix=CHECK_32_LE_AS_ARGS %s
+// CHECK_32_LE_AS_ARGS: "-mppc"
+// CHECK_32_LE_AS_ARGS-SAME: "-mlittle-endian"
+// CHECK_32_LE_AS_ARGS-SAME: "-many"
+
+// RUN: %clang -target powerpc64-unknown-linux-gnu %s -### -o %t.o -no-integrated-as 2>&1 | FileCheck -check-prefix=CHECK_64_BE_AS_ARGS %s
+// CHECK_64_BE_AS_ARGS: "-mppc64"
+// CHECK_64_BE_AS_ARGS-SAME: "-mbig-endian"
+// CHECK_64_BE_AS_ARGS-SAME: "-many"
+
+// RUN: %clang -target powerpc64le-unknown-linux-gnu %s -### -o %t.o -no-integrated-as 2>&1 | FileCheck -check-prefix=CHECK_64_LE_AS_ARGS %s
+// CHECK_64_LE_AS_ARGS: "-mppc64"
+// CHECK_64_LE_AS_ARGS-SAME: "-mlittle-endian"
+// CHECK_64_LE_AS_ARGS-SAME: "-mpower8"
 
 // OpenMP features
 // RUN: %clang -target powerpc-unknown-linux-gnu %s -### -fopenmp=libomp -o %t.o 2>&1 | FileCheck -check-prefix=CHECK_OPENMP_TLS %s