Bug 1203553 - Fix an MSVC warning in mozglue. r=glandium.

This lets us remove the ALLOW_COMPILER_WARNINGS=True flag.

mozglue/build/WindowsDllBlocklist.cpp

@@ -437,12 +437,16 @@ DllBlockSet::Add(const char* name, unsigned long long version)
 void
 DllBlockSet::Write(HANDLE file)
 {
-  AutoCriticalSection lock(&sLock);
-  DWORD nBytes;
+  // It would be nicer to use AutoCriticalSection here. However, its destructor
+  // might not run if an exception occurs, in which case we would never leave
+  // the critical section. (MSVC warns about this possibility.) So we
+  // enter and leave manually.
+  ::EnterCriticalSection(&sLock);
 
   // Because this method is called after a crash occurs, and uses heap memory,
   // protect this entire block with a structured exception handler.
   MOZ_SEH_TRY {
+    DWORD nBytes;
     for (DllBlockSet* b = gFirst; b; b = b->mNext) {
       // write name[,v.v.v.v];
       WriteFile(file, b->mName, strlen(b->mName), &nBytes, nullptr);
@@ -466,6 +470,8 @@ DllBlockSet::Write(HANDLE file)
     }
   }
   MOZ_SEH_EXCEPT (EXCEPTION_EXECUTE_HANDLER) { }
+
+  ::LeaveCriticalSection(&sLock);
 }
 
 static

mozglue/build/moz.build

@@ -94,9 +94,6 @@ DEFINES['IMPL_MFBT'] = True
 
 LDFLAGS += CONFIG['MOZ_GLUE_WRAP_LDFLAGS']
 
-if CONFIG['_MSC_VER']:
-    ALLOW_COMPILER_WARNINGS = True
-
 if CONFIG['OS_TARGET'] == 'Darwin':
     # On OSX 10.10.3, a dead lock happens in some cases involving dynamic
     # symbol resolution for symbols that jemalloc itself uses. While it