This results in a 17% improvement in the execution time of the "+" and
"-" benchmarks for fixnums.
* libguile/vm-i-scheme.c (ASM_ADD, ASM_SUB)[defined __x86_64__ &&
SCM_GNUC_PREREQ (4, 5)]: New macros.
(add)[defined ASM_ADD]: Use `ASM_ADD' for the fast path.
(sub)[defined ASM_SUB]: Use `ASM_SUB' for the fast path.
* test-suite/tests/numbers.test ("+")["fixnum + fixnum = bignum
(32-bit)", "fixnum + fixnum = bignum (64-bit)", "bignum + fixnum =
fixnum", "wrong type"]: New tests.
("-")["fixnum - fixnum = bignum (32-bit)", "fixnum - fixnum = bignum
(64-bit)", "bignum - fixnum = fixnum", "wrong type"]: New tests.
* test-suite/tests/00-initial-env.test ("goopsless")["+ wrong type
argument"]: Use `with-test-prefix/c&e' instead of `with-test-prefix'.
["- wrong type argument"]: New test prefix.
