pgsql: postgres: Use pg_{add,mul}_size_overflow()

postgres: Use pg_{add,mul}_size_overflow()

The backend implementations of add_size() and mul_size() can now make
use of the APIs provided in common/int.h.

Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/CAOYmi%2B%3D%2BpqUd2MUitvgW1pAJuXgG_TKCVc3_Ek7pe8z9nkf%2BAg%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/e2ceff13d83a85c634dc358b8291c7ae301e95e1

Modified Files
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src/backend/storage/ipc/shmem.c | 11 +++--------
1 file changed, 3 insertions(+), 8 deletions(-)