aix: Support GCC64 for AIX 7.1.

aix: Support GCC64 for AIX 7.1.

gcc/ChangeLog:

2020-07-24  David Edelsohn  <dje.gcc@gmail.com>
	    Clement Chigot  <clement.chigot@atos.net>

	* config.gcc (powerpc-ibm-aix7.1): Use t-aix64 and biarch64 for
	cpu_is_64bit.
	* config/rs6000/aix71.h (ASM_SPEC): Remove aix64 option.
	(ASM_SPEC32): New.
	(ASM_SPEC64): New.
	(ASM_CPU_SPEC): Remove vsx and altivec options.
	(CPP_SPEC_COMMON): Rename from CPP_SPEC.
	(CPP_SPEC32): New.
	(CPP_SPEC64): New.
	(CPLUSPLUS_CPP_SPEC): Rename to CPLUSPLUS_CPP_SPEC_COMMON..
	(TARGET_DEFAULT): Use 64 bit mask if BIARCH.
	(LIB_SPEC_COMMON): Rename from LIB_SPEC.
	(LIB_SPEC32): New.
	(LIB_SPEC64): New.
	(LINK_SPEC_COMMON): Rename from LINK_SPEC.
	(LINK_SPEC32): New.
	(LINK_SPEC64): New.
	(STARTFILE_SPEC): Add 64 bit version of crtcxa and crtdbase.
	(ASM_SPEC): Define 32 and 64 bit alternatives using DEFAULT_ARCH64_P.
	(CPP_SPEC): Same.
	(CPLUSPLUS_CPP_SPEC): Same.
	(LIB_SPEC): Same.
	(LINK_SPEC): Same.
	(SUBTARGET_EXTRA_SPECS): Add new 32/64 specs.
	* config/rs6000/aix72.h (TARGET_DEFAULT): Use 64 bit mask if BIARCH.
	* config/rs6000/defaultaix64.h: Delete.