setup.py: Explicilty use C99 for preprocessing

GCC 15 uses -std=c23 by default, which causes pycparser to error out
with "pycparser.plyparser.ParseError:
/usr/lib/gcc/x86_64-pc-linux-gnu/15/include/stddef.h:450:31:
before: nullptr_t". As pcyparser only supports completely C99,
this shouldn't be an issue.

Signed-off-by: Christopher Byrne <[email protected]>

setup.py

@@ -189,14 +189,15 @@ def get_mappings(self):
             pdata = preprocess_file(
                 header_path,
                 cpp_args=[
+                    "-std=c99",
                     "-D__builtin_va_list=char*",
                     "-D__extension__=",
                     "-D__attribute__(x)=",
                 ],
             )
         else:
             pdata = preprocess_file(
-                header_path, cpp_args=["-D__extension__=", "-D__attribute__(x)="]
+                header_path, cpp_args=["-std=c99", "-D__extension__=", "-D__attribute__(x)="]
             )
         parser = c_parser.CParser()
         ast = parser.parse(pdata, "tss2_tpm2_types.h")
@@ -218,6 +219,7 @@ def get_mappings(self):
                     pdata = preprocess_file(
                         policy_header_path,
                         cpp_args=[
+                            "-std=c99",
                             "-D__builtin_va_list=char*",
                             "-D__extension__=",
                             "-D__attribute__(x)=",
@@ -229,6 +231,7 @@ def get_mappings(self):
                     pdata = preprocess_file(
                         policy_header_path,
                         cpp_args=[
+                            "-std=c99",
                             "-D__extension__=",
                             "-D__attribute__(x)=",
                             "-D__float128=long double",