[base] Restore FT_MulFix inlining. * include/freetype.h (FT_MulFix): Unconditionally defined. * src/base/ftcalc.c [FT_MULFIX_ASSEMBLER]: Move code from here... * include/internal/ftcalc.h [FT_MULFIX_ASSEMBLER]: ... to here, which conditionally replaces the function with an inline version through the macro.