Bug 1295811 - Only run allocator checks when compile environment needed; r=glandium

Skipping them saves 1.5-2.0s from configure during an artifact build
on Windows.

MozReview-Commit-ID: ArCvrFP9UsD

--HG--
extra : rebase_source : fa580b69d1d96dc0631b626512273302647126f7

old-configure.in

@@ -2055,10 +2055,11 @@ if test "$ac_cv_i18n_lc_messages" = yes; then
 fi
 
 AC_HAVE_FUNCS(localeconv)
-fi # ! SKIP_COMPILER_CHECKS
 
 MOZ_CHECK_ALLOCATOR
 
+fi # ! SKIP_COMPILER_CHECKS
+
 TARGET_XPCOM_ABI=
 if test -n "${CPU_ARCH}" -a -n "${TARGET_COMPILER_ABI}"; then
     TARGET_XPCOM_ABI="${CPU_ARCH}-${TARGET_COMPILER_ABI}"