util: (trivial) add <stdint.h> include to slab.c
util: (trivial) add <stdint.h> include to slab.c

should fix "src/util/slab.c:57:13: error: ‘uint8_t’ undeclared"

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler