Fiasco.OC: forward CC, and CXX variables (fix #462)

When building the Fiasco.OC kernel, and L4Linux within the Genode build system,
forward the CC, and CXX variables. It might contain useful tools like ccache,
or distcc to speed up compilation. Moreover, don't delete the MAKEFLAGS when
building Fiasco.OC. It hinders parallel builds.

base-foc/src/kernel/target.inc

@@ -8,13 +8,14 @@ STARTUP_LIB   =
 $(TARGET): $(FIASCO)
 
 $(FOC_BUILD_DIR):
-	$(VERBOSE_MK) MAKEFLAGS= $(MAKE) SYSTEM_TARGET="$(CROSS_DEV_PREFIX)" \
-                                     $(VERBOSE_DIR) -C $(FIASCO_SRC) BUILDDIR=$@
+	$(VERBOSE_MK) $(MAKE) SYSTEM_TARGET="$(CROSS_DEV_PREFIX)" \
+                          $(VERBOSE_DIR) -C $(FIASCO_SRC) BUILDDIR=$@
 	$(VERBOSE)cp $(KERNEL_CONFIG) $@/globalconfig.out
 
 $(FIASCO): $(FOC_BUILD_DIR)
-	$(VERBOSE_MK) MAKEFLAGS= $(MAKE) SYSTEM_TARGET="$(CROSS_DEV_PREFIX)" \
-                                     $(VERBOSE_DIR) -C $(FOC_BUILD_DIR)
+	$(VERBOSE_MK) $(MAKE) SYSTEM_TARGET="$(CROSS_DEV_PREFIX)" \
+                          CC="$(CC)" CXX="$(CXX)" \
+                          $(VERBOSE_DIR) -C $(FOC_BUILD_DIR)
 	$(VERBOSE)ln -sf $@ $(BUILD_BASE_DIR)/bin/$(TARGET)
 
 clean cleanall:

ports-foc/mk/l4lx.mk

@@ -36,6 +36,7 @@ $(L4LX_BINARY): $(L4LX_CONFIG)
 	               -C $(REP_DIR)/contrib/$(LX_TARGET) \
 	               O=$(L4LX_BUILD) \
 	               CROSS_COMPILE="$(CROSS_DEV_PREFIX)" \
+	               CC="$(CC)" \
 	               KBUILD_VERBOSE=$(VERBOSE_LX_MK) \
 	               V=$(VERBOSE_LX_MK) \
 	               GENODE_INCLUDES="$(addprefix -I,$(INC_DIR))" \