binutils: fix build with gcc@10: (#16661)

The issue seems to be fixed in the development version already.

var/spack/repos/builtin/packages/binutils/package.py

@@ -124,4 +124,7 @@ def flag_handler(self, name, flags):
            and (self.compiler.name == 'fj' or self.compiler.name == 'clang')\
            and self.version <= ver('2.31.1'):
             flags.append('-Wno-narrowing')
+        elif name == 'cflags':
+            if self.spec.satisfies('@:2.34 %gcc@10:'):
+                flags.append('-fcommon')
         return (flags, None, None)