BLD: add static to std_c_flags test program (see gh23538)

Author: andyfaff

setup.py

@@ -293,7 +293,7 @@ def std_c_flags(cmd):
         ).get(compiler.compiler_type, ['-std=c99'])
 
         if not flags_is_required(compiler, False, flags, textwrap.dedent('''
-            inline int test_inline() { return 0; }
+            inline static int test_inline() { return 0; }
             int main(void)
             { return test_inline(); }
         ''')):