Less goto in ltrimWhitespace and rtrimWhitespace

Summary:
[Folly] Less `goto` in `ltrimWhitespace` and `rtrimWhitespace`.

The generated machine code remains unchanged for `g++ -O3` builds.

Generally, prefer to use `goto` in cases which cannot, or which can only arduously, be accomplished without it. In other words, reserve `goto` to cases where `goto` is necessary, rather than to cases where it saves one line.

Closes #732.

Reviewed By: andrewjcg

Differential Revision: D7027269

fbshipit-source-id: 91a4c5dba0e4c13dc727393799edc9b596cdb8b9

folly/String.cpp

@@ -132,15 +132,17 @@ StringPiece ltrimWhitespace(StringPiece sp) {
   // checked.  This configuration where we loop on the ' '
   // separately from oddspaces was empirically fastest.
 
-loop:
-  for (; !sp.empty() && sp.front() == ' '; sp.pop_front()) {
+  while (true) {
+    while (!sp.empty() && sp.front() == ' ') {
+      sp.pop_front();
     }
     if (!sp.empty() && is_oddspace(sp.front())) {
       sp.pop_front();
-    goto loop;
+      continue;
     }
 
     return sp;
+  }
 }
 
 StringPiece rtrimWhitespace(StringPiece sp) {
@@ -148,15 +150,17 @@ StringPiece rtrimWhitespace(StringPiece sp) {
   // checked.  This configuration where we loop on the ' '
   // separately from oddspaces was empirically fastest.
 
-loop:
-  for (; !sp.empty() && sp.back() == ' '; sp.pop_back()) {
+  while (true) {
+    while (!sp.empty() && sp.back() == ' ') {
+      sp.pop_back();
     }
     if (!sp.empty() && is_oddspace(sp.back())) {
       sp.pop_back();
-    goto loop;
+      continue;
     }
 
     return sp;
+  }
 }
 
 namespace {