[profile] Fix finding the first and last directory separators on Windows.

[ikudrin]

Summary

Windows allows using both types of directory separators in a path string,
but our code preferred backslashes to slashes.

[davidxl]

Is it possible to add a test case?

[ikudrin]

Unfortunately, we don't run the profile test suite on Windows.

[davidxl]

lgtm

lib/profile/InstrProfilingUtil.c

lprofApplyPathPrefix(char *Dest, const char *PathStr, const char *Prefix,
   if (!IS_DIR_SEPARATOR(Prefix[PrefixLen - 1]))
     Dest[PrefixLen++] = DIR_SEPARATOR;
 
   memcpy(Dest + PrefixLen, StrippedPathStr, strlen(StrippedPathStr) + 1);
 }
 
 COMPILER_RT_VISIBILITY const char *
 lprofFindFirstDirSeparator(const char *Path) {
-  const char *Sep;
-  Sep = strchr(Path, DIR_SEPARATOR);
-  if (Sep)
-    return Sep;
+  const char *Sep = strchr(Path, DIR_SEPARATOR);
 #if defined(DIR_SEPARATOR_2)
-  Sep = strchr(Path, DIR_SEPARATOR_2);
+  const char *Sep2 = strchr(Path, DIR_SEPARATOR_2);
+  if (!Sep || (Sep2 && Sep2 < Sep))
+    Sep = Sep2;
 #endif
   return Sep;
 }
 
 COMPILER_RT_VISIBILITY const char *lprofFindLastDirSeparator(const char *Path) {
-  const char *Sep;
-  Sep = strrchr(Path, DIR_SEPARATOR);
-  if (Sep)
-    return Sep;
+  const char *Sep = strrchr(Path, DIR_SEPARATOR);
 #if defined(DIR_SEPARATOR_2)
-  Sep = strrchr(Path, DIR_SEPARATOR_2);
+  const char *Sep2 = strrchr(Path, DIR_SEPARATOR_2);
+  if (!Sep || Sep2 > Sep)
+    Sep = Sep2;
 #endif
   return Sep;
 }
 
 COMPILER_RT_VISIBILITY int lprofSuspendSigKill() {
 #if defined(__linux__)
   int PDeachSig = 0;
   /* Temporarily suspend getting SIGKILL upon exit of the parent process. */