Make Unix.h:MakeErrMsg separate the prefix and errno string, so we get:

clang: error: unable to make temporary file: /etc/cc: can't make
  unique filename: Permission denied

instead of 

  clang: error: unable to make temporary file: /etc/cc: can't make
  unique filenamePermission denied

for example.

Also, audited the uses of MakeErrMsg to make the prefix strings
consistent (not end with newline/punctuation/space/": ").


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@69626 91177308-0d34-0410-b5e6-96231b3b80d8

lib/System/Unix/Unix.h

@@ -70,6 +70,9 @@
 /// string and the Unix error number given by \p errnum. If errnum is -1, the
 /// default then the value of errno is used.
 /// @brief Make an error message
+///
+/// If the error number can be converted to a string, it will be
+/// separated from prefix by ": ".
 static inline bool MakeErrMsg(
   std::string* ErrMsg, const std::string& prefix, int errnum = -1) {
   if (!ErrMsg)
@@ -94,7 +97,7 @@ static inline bool MakeErrMsg(
   // but, oh well, just use a generic message
   sprintf(buffer, "Error #%d", errnum);
 #endif
-  *ErrMsg = prefix + buffer;
+  *ErrMsg = prefix + ": " + buffer;
   return true;
 }