Makefile: support CROSS_COMPILE=armv7a-*

Gentoo uses armv7a-hardfloat-linux-gnueabi- as cross compiler prefix.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/Makefile b/Makefile
index 6eceeb3..00caaaf 100644
--- a/Makefile
+++ b/Makefile
@@ -30,7 +30,7 @@
   export HOST_ARCH=$(HOST_ARCH_X86)
 else ifneq (,$(findstring $(MK_ARCH), "aarch64" "armv8l"))
   export HOST_ARCH=$(HOST_ARCH_AARCH64)
-else ifneq (,$(findstring $(MK_ARCH), "arm" "armv7" "armv7l"))
+else ifneq (,$(findstring $(MK_ARCH), "arm" "armv7" "armv7a" "armv7l"))
   export HOST_ARCH=$(HOST_ARCH_ARM)
 else ifeq ("riscv32", $(MK_ARCH))
   export HOST_ARCH=$(HOST_ARCH_RISCV32)