Actual:
(gdb) ptype ENUM_BITFIELD(address_class)
No symbol "__extension__" in current context.

Expected:
(gdb) ptype enum address_class
type = enum address_class {LOC_UNDEF, LOC_CONST, LOC_STATIC, LOC_REGISTER,
LOC_ARG, LOC_REF_ARG, LOC_REGPARM_ADDR, LOC_LOCAL, LOC_TYPEDEF, LOC_LABEL,
LOC_BLOCK, LOC_CONST_BYTES, LOC_UNRESOLVED, LOC_OPTIMIZED_OUT, LOC_COMPUTED}

This breaks usage of macros in -g3 builds.

(gdb) info macro ENUM_BITFIELD
[...]
#define ENUM_BITFIELD(TYPE) __extension__ enum TYPE


But for example ({...}) still cannot get be parsed.