BUG #17424: Build failed on disabled GNUC in Clang environment CFLAGS= -O2 -fgnuc-version=0

The following bug has been logged on the website:

Bug reference: 17424
Logged by: arjun shetty
Email address: arjunshetty955(at)gmail(dot)com
PostgreSQL version: 14.2
Operating system: RHEL8.3
Description:

PostgreSQLv14.2 source compiled with build command
CC=clang CXX=clang++ ../configure --prefix=<install path> CFLAGS='-O2
-fgnuc-version=0' CXXFLAGS='-O2 -fno-builtin -fgnuc-version=0'
And observed build errors like:
/postgresql-14.2/build/../src/include/nodes/execnodes.h:1596:2: error:
unknown type name 'slock_t'; did you mean 'clock_t'?
slock_t mutex;
^~~~~~~
clock_t
/usr/include/x86_64-linux-gnu/bits/types/clock_t.h:7:19: note: 'clock_t'
declared here
typedef __clock_t clock_t;
postgresql-14.2/build/../src/backend/access/brin/brin.c:24

-fgnuc-version flag used to disable __builtin_xx functions in
PotgreSQLv14.2
Example :/postgresql14.2/contrib/cube/cubeparse.c +385

if defined YYCOPY_NEEDED && YYCOPY_NEEDED
/* Copy COUNT objects from SRC to DST. The source and destination do
not overlap. */
# ifndef YYCOPY
# if defined __GNUC__ && 1 < __GNUC__
# define YYCOPY(Dst, Src, Count) \
__builtin_memcpy (Dst, Src, (Count) * sizeof (*(Src))) /
# else
# define YYCOPY(Dst, Src, Count) \
do \
{ \
YYSIZE_T yyi; \
for (yyi = 0; yyi < (Count); yyi++) \
(Dst)[yyi] = (Src)[yyi]; \
} \
while (0)
# endif
# endif
#endif /*

please let me know how to disable __builtin__xxx functions in
PostgreSQLv14.2an build source code.