Problem: This keyword is used by GCC and Clang to prevent -Wpedantic
(and other options) from emitting warnings for many GNU C extensions.
This is used heavily in Alpine Linux through musl libc and
foritfy-headers. Without filtering the __extension__ keyword some type
definitions are duplicated. For example, timeval is defined once as
struct timeval { time_t tv_sec; suseconds_t tv_usec; };
and once as:
__extension__ struct timeval { time_t tv_sec; suseconds_t tv_usec; };
Without this patch, the LuaJIT C parser doesn't recognize that these
definitions are equivalent, causing unit test to fail on Alpine Linux.
Solution: Filter out the keyword in filter_complex_blocks.
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