ToolChains: Minor touchup to use correct type, avoid truncation.

Truncation happens regularly when find_first_not_of returns npos,
strings long enough to trigger bug here are implausible.

No functionality change intended (ignoring absurd string lengths).

llvm-svn: 172127
diff --git a/clang/lib/Driver/ToolChains.cpp b/clang/lib/Driver/ToolChains.cpp
index fa21760..03a01e3 100644
--- a/clang/lib/Driver/ToolChains.cpp
+++ b/clang/lib/Driver/ToolChains.cpp
@@ -952,7 +952,7 @@
   // And retains any patch number it finds.
   StringRef PatchText = GoodVersion.PatchSuffix = Second.second.str();
   if (!PatchText.empty()) {
-    if (unsigned EndNumber = PatchText.find_first_not_of("0123456789")) {
+    if (size_t EndNumber = PatchText.find_first_not_of("0123456789")) {
       // Try to parse the number and any suffix.
       if (PatchText.slice(0, EndNumber).getAsInteger(10, GoodVersion.Patch) ||
           GoodVersion.Patch < 0)