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@gmail.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.