Fix some rather confusing indentation and control flow in the errno

printing routine. This is made harder to see due to the surprising
formatting, inconsistent brace usage, and repeated conditions that all
test the same thing.

The only "consequence" of this bug is re-assigning 'str' to an empty
string when computing the error string for an error number of 0 in the
event of a non-GNU strerror_r routine. So, nothing to see here other
than cleanup. It did help me find PR17055 in clang-format though.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189734 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Support/Errno.cpp

@@ -39,28 +39,27 @@ std::string StrError(int errnum) {
   char buffer[MaxErrStrLen];
   buffer[0] = '\0';
   std::string str;
+  if (errnum == 0)
+    return str;
+
 #ifdef HAVE_STRERROR_R
   // strerror_r is thread-safe.
-  if (errnum)
-# if defined(__GLIBC__) && defined(_GNU_SOURCE)
-    // glibc defines its own incompatible version of strerror_r
-    // which may not use the buffer supplied.
-    str = strerror_r(errnum,buffer,MaxErrStrLen-1);
-# else
-    strerror_r(errnum,buffer,MaxErrStrLen-1);
-    str = buffer;
-# endif
+#if defined(__GLIBC__) && defined(_GNU_SOURCE)
+  // glibc defines its own incompatible version of strerror_r
+  // which may not use the buffer supplied.
+  str = strerror_r(errnum, buffer, MaxErrStrLen - 1);
+#else
+  strerror_r(errnum, buffer, MaxErrStrLen - 1);
+  str = buffer;
+#endif
 #elif HAVE_DECL_STRERROR_S // "Windows Secure API"
-    if (errnum) {
-      strerror_s(buffer, MaxErrStrLen - 1, errnum);
-      str = buffer;
-    }
+  strerror_s(buffer, MaxErrStrLen - 1, errnum);
+  str = buffer;
 #elif defined(HAVE_STRERROR)
   // Copy the thread un-safe result of strerror into
   // the buffer as fast as possible to minimize impact
   // of collision of strerror in multiple threads.
-  if (errnum)
-    str = strerror(errnum);
+  str = strerror(errnum);
 #else
   // Strange that this system doesn't even have strerror
   // but, oh well, just use a generic message