v1.0: host-cpu-c-abi: Avoid use of 'grep -E' on OpenIndiana.

* m4/asm-underscore.m4 (gl_ASM_SYMBOL_PREFIX): Require AC_PROG_EGREP,
and use $EGREP instead of 'grep -E'.
* m4/host-cpu-c-abi.m4 (gl_HOST_CPU_C_ABI): Use 'grep' instead of
'grep -E'.