scons: Disable MSVC warnings about inconsistent function annotation.

Somehow, merely including any of the *intrin.h headers causes dozens of
this warnings (when compiling pretty much every source file).  MSVC does
not always complain the same -- so it's possible we're doing something
weird --, but silence these warnings in the meanwhile.

Reviewed-by: Brian Paul <brianp@vmware.com>

scons/gallium.py

@@ -549,6 +549,7 @@ def generate(env):
             env.Append(CCFLAGS = [
                 '/analyze',
                 #'/analyze:log', '${TARGET.base}.xml',
+                '/wd28251', # Inconsistent annotation for function
             ])
         if env['clang']:
             # scan-build will produce more comprehensive output