Don't shadow global variable index:
cc1: warnings being treated as errors
raqm.c: In function '_raqm_u32_to_u8_index':
raqm.c:1602: warning: declaration of 'index' shadows a global declaration
/usr/include/strings.h:62: warning: shadowed declaration is here
raqm.c: In function '_raqm_u8_to_u32_index':
raqm.c:1619: warning: declaration of 'index' shadows a global declaration
/usr/include/strings.h:62: warning: shadowed declaration is here
raqm.c: In function 'raqm_index_to_position':
raqm.c:1658: warning: declaration of 'index' shadows a global declaration
/usr/include/strings.h:62: warning: shadowed declaration is here
raqm.c: In function 'raqm_position_to_index':
raqm.c:1752: warning: declaration of 'index' shadows a global declaration
/usr/include/strings.h:62: warning: shadowed declaration is here

Fails to build with base GCC.