pgsql: makefile: use proper linker flags for C++ compiles

makefile: use proper linker flags for C++ compiles

Add CFLAGS_SL flags for C++ compiles, which adds needed -fPIC linker
flag.

Reported-by: Oleksii Kliukin

Discussion: /messages/by-id/E4A49A6B-621B-4830-A374-970EBB7D1328@hintbits.com

Backpatch-through: 10 only

Branch
------
REL_10_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/f1e8362aefc866a6f75b6b41edccd03d51235d17

Modified Files
--------------
src/Makefile.shlib | 1 +
1 file changed, 1 insertion(+)