[profile] Add underscore to /alternatename for Win/x86

[aeubanks]

Summary

/alternatename should use the mangled name. On x86 we need an extra
underscore.

Copied from sanitizer_win_defs.h

Fixes https://crbug.com/1233589.

[aeubanks]

not really sure how to add a test for this

[phosek]

LGTM thanks for catching this! This is another reason to do https://lists.llvm.org/pipermail/llvm-dev/2021-July/151789.html since if we just used WIN_WEAK_ALIAS we could have avoid this issue.

compiler-rt/lib/profile/InstrProfilingFile.c

597–606

Could we reverse the condition just like what sanitizer_win_defs.h does.

[aeubanks]

compiler-rt/lib/profile/InstrProfilingFile.c

597–606

I can do that, but this was copied directly from sanitizer_win_defs.h, sanitizer_win_defs.h doesn't use _WIN64

[phosek]

compiler-rt/lib/profile/InstrProfilingFile.c

597–606

Never mind, I was looking at older version but it looks like sanitizer_win_defs.h switched to this version to support MinGW.

compiler-rt/lib/profile/InstrProfilingFile.c

 #define INSTR_PROF_PROFILE_COUNTER_BIAS_DEFAULT_VAR                            \
   INSTR_PROF_CONCAT(INSTR_PROF_PROFILE_COUNTER_BIAS_VAR, _default)
 intptr_t INSTR_PROF_PROFILE_COUNTER_BIAS_DEFAULT_VAR = 0;
 
 /* This variable is a weak external reference which could be used to detect
  * whether or not the compiler defined this symbol. */
 #if defined(_WIN32)
 COMPILER_RT_VISIBILITY extern intptr_t INSTR_PROF_PROFILE_COUNTER_BIAS_VAR;
-#pragma comment(linker, "/alternatename:"                                      \
-      INSTR_PROF_QUOTE(INSTR_PROF_PROFILE_COUNTER_BIAS_VAR) "="                \
+#if defined(_M_IX86) || defined(__i386__)
+#define WIN_SYM_PREFIX "_"
+#else
+#define WIN_SYM_PREFIX
+#endif
+#pragma comment(                                                               \
+    linker, "/alternatename:" WIN_SYM_PREFIX INSTR_PROF_QUOTE(                 \
+                INSTR_PROF_PROFILE_COUNTER_BIAS_VAR) "=" WIN_SYM_PREFIX        \
                 INSTR_PROF_QUOTE(INSTR_PROF_PROFILE_COUNTER_BIAS_DEFAULT_VAR))
 #else
 COMPILER_RT_VISIBILITY extern intptr_t INSTR_PROF_PROFILE_COUNTER_BIAS_VAR
     __attribute__((weak, alias(INSTR_PROF_QUOTE(
                              INSTR_PROF_PROFILE_COUNTER_BIAS_DEFAULT_VAR))));
 #endif
 
 static int writeMMappedFile(FILE *OutputFile, char **Profile) {
   if (!OutputFile)
     return -1;