build: Move TARGET_* assignments earlier

build: Move TARGET_* assignments earlier

On a 32-bit SPARC userland, configure fails to compile assembly and the
build fails:

    checking for options to compile assembly... configure: error: could not compile assembly

config.log shows:

    asm-tests/sparc64.S: Assembler messages:
    asm-tests/sparc64.S:5: Error: Architecture mismatch on "lduw [%o4+4],%o4".
    asm-tests/sparc64.S:5: (Requires v9|v9a|v9b|v9c|v9d|v9e|v9v|v9m|m8; requested architecture is sparclite.)
    asm-tests/sparc64.S:7: Error: Architecture mismatch on "stw %o5,[%o3]".
    asm-tests/sparc64.S:7: (Requires v9|v9a|v9b|v9c|v9d|v9e|v9v|v9m|m8; requested architecture is sparclite.)
    asm-tests/sparc64.S:8: Error: Architecture mismatch on "bne,pt %icc,1b ,pt %icc,1b".
    asm-tests/sparc64.S:8: (Requires v9|v9a|v9b|v9c|v9d|v9e|v9v|v9m|m8; requested architecture is sparclite.)

Simply moving these blocks earlier in configure.ac is sufficient to
ensure that the tests are executed with the appropriate flags
(specifically -m64 in this case).

Bug: https://bugs.gentoo.org/667850

Signed-off-by: Mike Gilbert <floppym@gentoo.org>
Signed-off-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Tested-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>