Makefile.uk: Condition header inclusion on Kconfig

Previously musl would add its headers to the include path
unconditionally when its Makefile would be included.
This change conditions this inclusion on whether musl is enabled via
Kconfig.

Signed-off-by: Andrei Tatar <andrei@unikraft.io>

Makefile.rules

@@ -27,8 +27,8 @@ LIBMUSL_CINCLUDES-y += $$(LIBMUSL_$(call uc,$(1))_INCLUDES-y)
 LIBMUSL_CXXINCLUDES-y += $$(LIBMUSL_$(call uc,$(1))_INCLUDES-y)
 
 # includes for using libmusl
-CINCLUDES-y += -I$(LIBMUSL_BUILD)/include/$(1)/include
-CXXINCLUDES-y += -I$(LIBMUSL_BUILD)/include/$(1)/include
+CINCLUDES-$(CONFIG_LIBMUSL) += -I$(LIBMUSL_BUILD)/include/$(1)/include
+CXXINCLUDES-$(CONFIG_LIBMUSL) += -I$(LIBMUSL_BUILD)/include/$(1)/include
 
 # Append the sub library directory to the include path
 $(LIBMUSL_BUILD)/.prepared: $(subst $(LIBMUSL),$(LIBMUSL_BUILD)/include/$(1),$(2))

Makefile.uk

@@ -98,8 +98,8 @@ LIBMUSL_COMPFLAGS-y += -I$(LIBMUSL)/arch/$(MUSL_ARCH)
 LIBMUSL_COMPFLAGS-y += -I$(LIBMUSL)/src/include
 LIBMUSL_COMPFLAGS-y += -I$(LIBMUSL)/src/internal
 
-CINCLUDES-y    += $(LIBMUSL_GLOBAL_INCLUDES-y)
-CXXINCLUDES-y  += $(LIBMUSL_GLOBAL_INCLUDES-y)
+CINCLUDES-$(CONFIG_LIBMUSL)    += $(LIBMUSL_GLOBAL_INCLUDES-y)
+CXXINCLUDES-$(CONFIG_LIBMUSL)  += $(LIBMUSL_GLOBAL_INCLUDES-y)
 
 ################################################################################
 # Musl-specific Targets
@@ -154,8 +154,8 @@ LIBMUSL_CFLAGS-y += $(LIBMUSL_HDRS_FLAGS-y)
 LIBMUSL_CFLAGS-y += -ffreestanding
 
 # We globally switch off warnings that are caused by musl's public headers
-CFLAGS += $(LIBMUSL_HDRS_FLAGS-y)
-CXXFLAGS += $(LIBMUSL_HDRS_FLAGS-y)
+CFLAGS-$(CONFIG_LIBMUSL) += $(LIBMUSL_HDRS_FLAGS-y)
+CXXFLAGS-$(CONFIG_LIBMUSL) += $(LIBMUSL_HDRS_FLAGS-y)
 
 ################################################################################
 # OS dependencies code - Glue between Unicore and musl