base-linux: configurable host toolchain

This commit uses CUSTOM_HOST_CC/CUSTOM_HOST_CXX instead of hardcoded
commands and introduces HOST_DEV_PREFIX.

Original patch by Roman Iten and Pirmin Duss.

Issue #3466

repos/base-linux/lib/import/import-lx_hybrid.mk

@@ -7,7 +7,7 @@ include $(call select_from_repositories,lib/import/import-syscall-linux.mk)
 # Manually supply all library search paths of the host compiler to our tool
 # chain.
 #
-HOST_LIB_SEARCH_DIRS = $(shell cc $(CC_MARCH) -print-search-dirs | grep libraries |\
+HOST_LIB_SEARCH_DIRS = $(shell $(CUSTOM_HOST_CC) $(CC_MARCH) -print-search-dirs | grep libraries |\
                                sed "s/.*=//"   | sed "s/:/ /g" |\
                                sed "s/\/ / /g" | sed "s/\/\$$//")
 #
@@ -18,7 +18,7 @@ HOST_LIB_SEARCH_DIRS = $(shell cc $(CC_MARCH) -print-search-dirs | grep librarie
 # is appended to the include directory list.
 #
 HOST_INC_DIR += $(shell echo "int main() {return 0;}" |\
-                        LANG=C $(CXX) -x c++ -v -E - 2>&1 |\
+                        LANG=C $(CXX) -x $(CUSTOM_HOST_CXX) -v -E - 2>&1 |\
                         sed '/^\#include <\.\.\.> search starts here:/,/^End of search list/!d' |\
                         grep "include-fixed")
 
@@ -68,11 +68,11 @@ endif
 LD_TEXT_ADDR     ?=
 LD_SCRIPT_STATIC ?=
 
-EXT_OBJECTS += $(shell cc $(CC_MARCH) -print-file-name=crt1.o)
-EXT_OBJECTS += $(shell cc $(CC_MARCH) -print-file-name=crti.o)
+EXT_OBJECTS += $(shell $(CUSTOM_HOST_CC) $(CC_MARCH) -print-file-name=crt1.o)
+EXT_OBJECTS += $(shell $(CUSTOM_HOST_CC) $(CC_MARCH) -print-file-name=crti.o)
 EXT_OBJECTS += $(shell $(CUSTOM_CC) $(CC_MARCH) -print-file-name=crtbegin.o)
 EXT_OBJECTS += $(shell $(CUSTOM_CC) $(CC_MARCH) -print-file-name=crtend.o)
-EXT_OBJECTS += $(shell cc $(CC_MARCH) -print-file-name=crtn.o)
+EXT_OBJECTS += $(shell $(CUSTOM_HOST_CC) $(CC_MARCH) -print-file-name=crtn.o)
 
 LX_LIBS_OPT += -lgcc -lgcc_s -lsupc++ -lc -lpthread
 
@@ -105,7 +105,7 @@ endif
 LD_LIBGCC = $(LX_LIBS_OPT)
 
 # use the host c++ for linking to find shared libraries in DT_RPATH library paths
-LD_CMD = c++
+LD_CMD = $(CUSTOM_HOST_CXX)
 
 # disable format-string security checks, which prevent non-literal format strings
 CC_OPT += -Wno-format-security
@@ -115,7 +115,7 @@ CC_OPT += -Wno-format-security
 # Ubuntu 16.10 or newer)
 #
 CXX_LINK_OPT_NO_PIE := $(shell \
-	(echo "int main(){}" | $(LD_CMD) -no-pie -x c++ - -o /dev/null >& /dev/null \
+	(echo "int main(){}" | $(LD_CMD) -no-pie -x $(CUSTOM_HOST_CXX) - -o /dev/null >& /dev/null \
 	&& echo "-no-pie") || true)
 CXX_LINK_OPT += $(CXX_LINK_OPT_NO_PIE)
 

repos/base-linux/lib/import/import-syscall-linux.mk

@@ -1,8 +1,9 @@
 HOST_INC_DIR += $(dir $(call select_from_repositories,src/lib/syscall/linux_syscalls.h))
+HOST_INC_DIR += $(dir $(CUSTOM_HOST_CC))/../$(shell $(CUSTOM_HOST_CC) -dumpmachine)/libc/usr/include
 HOST_INC_DIR += /usr/include
 
 # needed for Ubuntu >= 11.04
-HOST_INC_DIR += /usr/include/$(shell gcc -dumpmachine)
+HOST_INC_DIR += /usr/include/$(shell $(CUSTOM_HOST_CC) -dumpmachine)
 
 #
 # Explicitly add some well-known paths as the dumpmachine magic above does not

repos/base-linux/lib/mk/spec/arm/base-linux.mk

@@ -8,4 +8,4 @@ SRC_CC += cpu/arm/cache.cc
 
 LIBS += timeout-arm
 
-include $(REP_DIR)/lib/mk/base.mk
+include $(REP_DIR)/lib/mk/base-linux.mk

repos/base/mk/global.mk

@@ -23,7 +23,8 @@ CUSTOM_OBJCOPY  ?= $(CROSS_DEV_PREFIX)objcopy
 CUSTOM_RANLIB   ?= $(CROSS_DEV_PREFIX)ranlib
 CUSTOM_STRIP    ?= $(CROSS_DEV_PREFIX)strip
 CUSTOM_GNATBIND ?= $(CROSS_DEV_PREFIX)gnatbind
-CUSTOM_HOST_CC  ?= gcc
+CUSTOM_HOST_CC  ?= $(HOST_DEV_PREFIX)gcc
+CUSTOM_HOST_CXX ?= $(HOST_DEV_PREFIX)g++
 CUSTOM_ADA_CC   ?= $(CUSTOM_CC)
 CUSTOM_ALI2DEP  ?= $(CROSS_DEV_PREFIX)ali2dep