Try to use __builtin_ffsl if ffsl is unavailable.

Some platforms (like those using Newlib) don't have ffs/ffsl.  This
commit adds a check to configure.ac for __builtin_ffsl if ffsl isn't
found.  __builtin_ffsl performs the same function as ffsl, and has the
added benefit of being available on any platform utilizing
Gcc-compatible compiler.

This change does not address the used of ffs in the MALLOCX_ARENA()
macro.

include/jemalloc/internal/jemalloc_internal.h.in

@@ -215,6 +215,9 @@ static const bool config_ivsalloc =
 #  ifdef __tile__
 #    define LG_QUANTUM		4
 #  endif
+#  ifdef __le32__
+#    define LG_QUANTUM		4
+#  endif
 #  ifndef LG_QUANTUM
 #    error "No LG_QUANTUM definition for architecture; specify via CPPFLAGS"
 #  endif