Set arm_arch as well

Either overlooked or added after we make the GN switch.

Change-Id: I93bfc27c2e71165901c2046ab2ea902d9dad39d3
Reviewed-by: Michal Klocek <michal.klocek@qt.io>

src/core/config/linux.pri

@@ -44,6 +44,7 @@ contains(QT_ARCH, "arm") {
     !isEmpty(MFLOAT): gn_args += arm_float_abi=\"$$MFLOAT\"
 
     MARCH = $$extractCFlag("-march=.*")
+    !isEmpty(MARCH): gn_args += arm_arch=\"$$MARCH\"
 
     MARMV = $$replace(MARCH, "armv",)
     !isEmpty(MARMV) {