scons: Unbreak mingw builds.

scons/gallium.py

@@ -438,7 +438,7 @@ def generate(env):
             linkflags += ['-m32']
         if env['machine'] == 'x86_64':
             linkflags += ['-m64']
-    if platform == 'windows':
+    if platform == 'windows' and msvc:
         # See also:
         # - http://msdn2.microsoft.com/en-us/library/y0zzbyt4.aspx
         linkflags += [

scons/generic.py

@@ -517,7 +517,7 @@ def generate(env):
             linkflags += ['-m32']
         if env['machine'] == 'x86_64':
             linkflags += ['-m64']
-    if platform == 'windows':
+    if platform == 'windows' and msvc:
         # See also:
         # - http://msdn2.microsoft.com/en-us/library/y0zzbyt4.aspx
         linkflags += [