syntax fix

Author: martin-frbg

Makefile.arm64

@@ -61,7 +61,7 @@ endif
 ifeq ($(CORE), ARMV9SME)
 CCOMMON_OPT += -march=armv9-a+sve2+sme
 FCOMMON_OPT += -march=armv9-a+sve2
-if defined(OS_WINDOWS)
+ifdef OS_WINDOWS
 ifeq ($(C_COMPILER), CLANG)
 CCOMMON_OPT += --aarch64-stack-hazard-size=0
 endif