[NFCI][asm][i386/x86-64] Enable AT&T syntax explicitly (#164453)

Implementation files using the Intel syntax explicitly specify it.
Do the same for the few files using AT&T syntax.

This also enables building LLVM with `-mllvm -x86-asm-syntax=intel` in one's Clang config files
(i.e. a global preference for Intel syntax).

No functional change intended.

compiler-rt/lib/asan/asan_rtl_x86_64.S

@@ -5,6 +5,7 @@
 #include "sanitizer_common/sanitizer_platform.h"
 
 .file "asan_rtl_x86_64.S"
+.att_syntax
 
 #define NAME(n, reg, op, s, i) n##_##op##_##i##_##s##_##reg
 

compiler-rt/lib/builtins/assembly.h

@@ -337,4 +337,8 @@
 #endif
 #endif
 
+#if defined(__i386__) || defined(__amd64__)
+.att_syntax
+#endif
+
 #endif // COMPILERRT_ASSEMBLY_H

compiler-rt/lib/hwasan/hwasan_setjmp_x86_64.S

@@ -30,6 +30,7 @@
 
 .section .text
 .file "hwasan_setjmp_x86_64.S"
+.att_syntax
 
 .global ASM_WRAPPER_NAME(setjmp)
 ASM_TYPE_FUNCTION(ASM_WRAPPER_NAME(setjmp))

compiler-rt/lib/orc/elfnix_tls.x86-64.S

@@ -13,6 +13,7 @@
 
 // The content of this file is x86_64-only
 #if defined(__x86_64__)
+.att_syntax
 
 #define REGISTER_SAVE_SPACE_SIZE        512
 

compiler-rt/lib/orc/sysv_reenter.x86-64.S

@@ -12,6 +12,7 @@
 
 // The content of this file is x86_64-only
 #if defined(__x86_64__)
+.att_syntax
 
 // Save all GRPS except %rsp.
 // This value is also subtracted from %rsp below, despite the fact that %rbp

compiler-rt/lib/sanitizer_common/sanitizer_common_interceptors_vfork_i386.inc.S

@@ -2,6 +2,8 @@
 
 #include "sanitizer_common/sanitizer_asm.h"
 
+.att_syntax
+
 .comm _ZN14__interception10real_vforkE,4,4
 .globl ASM_WRAPPER_NAME(vfork)
 ASM_TYPE_FUNCTION(ASM_WRAPPER_NAME(vfork))

compiler-rt/lib/sanitizer_common/sanitizer_common_interceptors_vfork_x86_64.inc.S

@@ -2,6 +2,8 @@
 
 #include "sanitizer_common/sanitizer_asm.h"
 
+.att_syntax
+
 .comm _ZN14__interception10real_vforkE,8,8
 .globl ASM_WRAPPER_NAME(vfork)
 ASM_TYPE_FUNCTION(ASM_WRAPPER_NAME(vfork))

compiler-rt/lib/tsan/rtl/tsan_rtl_amd64.S

@@ -3,6 +3,8 @@
 
 #include "sanitizer_common/sanitizer_asm.h"
 
+.att_syntax
+
 #if !defined(__APPLE__)
 .section .text
 #else

libunwind/src/UnwindRegistersRestore.S

@@ -25,6 +25,8 @@
 #if !defined(__USING_SJLJ_EXCEPTIONS__)
 
 #if defined(__i386__)
+.att_syntax
+
 DEFINE_LIBUNWIND_FUNCTION(__libunwind_Registers_x86_jumpto)
 #
 # extern "C" void __libunwind_Registers_x86_jumpto(Registers_x86 *);
@@ -69,6 +71,7 @@ DEFINE_LIBUNWIND_FUNCTION(__libunwind_Registers_x86_jumpto)
   # skip gs
 
 #elif defined(__x86_64__) && !defined(__arm64ec__)
+.att_syntax
 
 DEFINE_LIBUNWIND_FUNCTION(__libunwind_Registers_x86_64_jumpto)
 #

libunwind/src/UnwindRegistersSave.S

@@ -25,6 +25,7 @@
 #if !defined(__USING_SJLJ_EXCEPTIONS__)
 
 #if defined(__i386__)
+.att_syntax
 
 #
 # extern int __unw_getcontext(unw_context_t* thread_state)
@@ -109,6 +110,7 @@ DEFINE_LIBUNWIND_FUNCTION("#__unw_getcontext")
   .text
 
 #elif defined(__x86_64__)
+.att_syntax
 
 #
 # extern int __unw_getcontext(unw_context_t* thread_state)

openmp/runtime/src/z_Linux_asm.S

@@ -18,6 +18,7 @@
 #include "kmp_config.h"
 
 #if KMP_ARCH_X86 || KMP_ARCH_X86_64
+.att_syntax
 
 # if defined(__ELF__) && defined(__CET__) && defined(__has_include)
 # if __has_include(<cet.h>)