php-maxminddb: fix build with GCC-based architectures

Add USES=compiler:c11 to fix build:
/wrkdirs/usr/ports/devel/php-maxminddb/work-php71/MaxMind-DB-Reader-php-1.1.0/ext/maxminddb.c:430: error: 'MMDB_entry_data_s' has no member named 'uint128'
/wrkdirs/usr/ports/devel/php-maxminddb/work-php71/MaxMind-DB-Reader-php-1.1.0/ext/maxminddb.c:431: error: 'MMDB_entry_data_s' has no member named 'uint128'

Approved by: mentors (implicit approval)