Hack: Allow to disable armv6+ membarrier check

If building for armv5+ on armv6+, the armv6+ check will succeed but the resulting
binaries won't work on armv5 so allow to force to disable the check.
[ Would be far better to do this kind of stuff on runtime not build time ]

Rtp
Index: mono-2.10.9/configure.in
===================================================================
--- mono-2.10.9.orig/configure.in
+++ mono-2.10.9/configure.in
@@ -2669,6 +2669,9 @@ if test ${TARGET} = ARM && test x$cross_
 	CPPFLAGS="$CPPFLAGS -DARM_FPU_$fpu=1"
 	unset fpu
 
+	AC_ARG_WITH(armv6,  [  --with-armv6=yes,no If you want to check for armv6+ membarrier (defaults to yes)],[], [with_armv6=yes])
+
+	if test x$with_armv6 = xyes; then
 	AC_MSG_CHECKING(for ARMV6)
 	AC_TRY_RUN([
 		int main () { __asm__ __volatile__ ("mcr p15, 0, %0, c7, c10, 5" : : "r" (0) : "memory"); return 0; }
@@ -2680,6 +2683,7 @@ if test ${TARGET} = ARM && test x$cross_
 	   # libgc's gc_locks.h depends on this
 	   NESTED_LIBGC_FLAGS="$NESTED_LIBGC_FLAGS -DHAVE_ARMV6"
 	fi
+	fi
 fi
 
 if test ${TARGET} = unknown; then