Fix strict compiler warning in the gflags code

extern/gflags/README.blender

@@ -18,6 +18,8 @@ Local modifications:
 - Applied some modifications from fork https://github.com/Nazg-Gul/gflags.git
   (see https://github.com/gflags/gflags/pull/129)
 
-- Avoid attemot of acquiring mutex lock in FlagRegistry::GlobalRegistry when
+- Avoid attempt of acquiring mutex lock in FlagRegistry::GlobalRegistry when
   doing static flags initialization. See d81dd2d in Blender repository.
 
+- Made `google::{anonymous}::FlagValue::ValueSize() const` inlined, so it does
+  not trigger strict compiler warning.

extern/gflags/src/gflags.cc

@@ -218,7 +218,7 @@ class FlagValue {
   bool Equal(const FlagValue& x) const;
   FlagValue* New() const;   // creates a new one with default value
   void CopyFrom(const FlagValue& x);
-  int ValueSize() const;
+  inline int ValueSize() const;
 
   // Calls the given validate-fn on value_buffer_, and returns
   // whatever it returns.  But first casts validate_fn_proto to a
@@ -443,7 +443,7 @@ void FlagValue::CopyFrom(const FlagValue& x) {
   }
 }
 
-int FlagValue::ValueSize() const {
+inline int FlagValue::ValueSize() const {
   if (type_ > FV_MAX_INDEX) {
     assert(false);  // unknown type
     return 0;