Bug 1523851 - Remove the AC_FUNC_MEMCMP test. r=froydnj

Autoconf 2.13 documentation says: "If the memcmp function is not
available, or does not work on 8-bit data (like the one on SunOS 4.1.3),
add `memcmp.o' to output variable LIBOBJS."

The documentation of more recent versions of autoconf also mention NeXT
x86 OpenStep, and say "This macro is obsolescent, as current systems
have a working memcmp. New programs need not use this macro."

We're also not using LIBOBJS, so, even if somehow some machine had the
test detect something weird going on, the result of the test wouldn't
have an effect on the build anyways.

Apart from that, it's also one of the few tests that relies on actually
running a compiled binary during configure, which requires some
autoconf-specific definition of cross-compilation (where --target=i686
--host=x86_64 is not cross-compilation), and we're better off getting
rid of such tests completely.

Depends on D18054

Differential Revision: https://phabricator.services.mozilla.com/D18055

--HG--
extra : moz-landing-system : lando

js/src/old-configure.in

@@ -1000,7 +1000,6 @@ fi
 
 dnl Checks for library functions.
 dnl ========================================================
-AC_FUNC_MEMCMP
 AC_CHECK_FUNCS([getc_unlocked _getc_nolock gmtime_r localtime_r pthread_getname_np pthread_get_name_np])
 
 dnl check for clock_gettime(), the CLOCK_MONOTONIC clock

old-configure.in

@@ -1275,7 +1275,6 @@ fi
 
 dnl Checks for library functions.
 dnl ========================================================
-AC_FUNC_MEMCMP
 AC_CHECK_FUNCS(stat64 lstat64 truncate64 statvfs64 statvfs statfs64 statfs getpagesize gmtime_r localtime_r arc4random arc4random_buf mallinfo gettid lchown setpriority strerror syscall)
 
 dnl check for clock_gettime(), the CLOCK_MONOTONIC clock