scons: Make PIPE_ALIGN_VAR() of static/global vars work on MinGW.

Workaround http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37216
diff --git a/scons/gallium.py b/scons/gallium.py
index dd72754..388f446 100644
--- a/scons/gallium.py
+++ b/scons/gallium.py
@@ -282,6 +282,9 @@
                 ccflags += [
                     '-mmmx', '-msse', '-msse2', # enable SIMD intrinsics
                 ]
+            if platform == 'windows':
+                # Workaround http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37216
+                ccflags += ['-fno-common']
             if distutils.version.LooseVersion(ccversion) >= distutils.version.LooseVersion('4.2'):
                 ccflags += [
                     '-mstackrealign', # ensure stack is aligned