Makefile: Remove unsupported cflag

Clang throws an error stating that '-Wno-undefined-optimized' is
unsupported. Hence, drop this flag.

Issue: FP3-A11#330
Change-Id: I469abcf9b22a846e6051008926ac0dd7ea65fc18
diff --git a/Makefile b/Makefile
index ed160a0..3b752a9 100644
--- a/Makefile
+++ b/Makefile
@@ -531,7 +531,6 @@
 KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
 KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
 KBUILD_CFLAGS += $(call cc-disable-warning, duplicate-decl-specifier)
-KBUILD_CFLAGS += -Wno-undefined-optimized
 KBUILD_CFLAGS += -Wno-tautological-constant-out-of-range-compare
 KBUILD_CFLAGS += $(call cc-option, -Wno-sometimes-uninitialized)
 KBUILD_CFLAGS += -Wno-asm-operand-widths