Makefile: generate CMake toolchain-file in $(O)

A CMake toolchain-file makes it easy to develop CMake-based packages
outside of Buildroot. Just give the toolchain-file to CMake via the
-DCMAKE_TOOLCHAIN_FILE=... option.

Signed-off-by: Bjørn Forsman <bjorn.forsman@gmail.com>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

Makefile

@@ -363,7 +363,7 @@ $(TARGETS_ALL): __real_tgt_%: $(BASE_TARGETS) %
 dirs: $(DL_DIR) $(TOOLCHAIN_DIR) $(BUILD_DIR) $(STAGING_DIR) $(TARGET_DIR) \
 	$(HOST_DIR) $(BR2_DEPENDS_DIR) $(BINARIES_DIR) $(STAMP_DIR)
 
-$(BASE_TARGETS): dirs
+$(BASE_TARGETS): dirs $(O)/toolchainfile.cmake
 
 $(BUILD_DIR)/buildroot-config/auto.conf: $(CONFIG_DIR)/.config
 	$(MAKE) $(EXTRAMAKEARGS) silentoldconfig
@@ -372,6 +372,21 @@ prepare: $(BUILD_DIR)/buildroot-config/auto.conf
 
 world: prepare dependencies dirs $(BASE_TARGETS) $(TARGETS_ALL)
 
+$(O)/toolchainfile.cmake:
+	@echo -en "\
+	set(CMAKE_SYSTEM_NAME Linux)\n\
+	set(CMAKE_C_COMPILER $(CMAKE_TARGET_CC))\n\
+	set(CMAKE_CXX_COMPILER $(CMAKE_TARGET_CXX))\n\
+	set(CMAKE_C_FLAGS \"\$${CMAKE_C_FLAGS} $(CMAKE_TARGET_CFLAGS)\" CACHE STRING \"Buildroot CFLAGS\" FORCE)\n\
+	set(CMAKE_CXX_FLAGS \"\$${CMAKE_CXX_FLAGS} $(CMAKE_TARGET_CXXFLAGS)\" CACHE STRING \"Buildroot CXXFLAGS\" FORCE)\n\
+	set(CMAKE_INSTALL_SO_NO_EXE 0)\n\
+	set(CMAKE_PROGRAM_PATH \"$(HOST_DIR)/usr/bin\")\n\
+	set(CMAKE_FIND_ROOT_PATH \"$(STAGING_DIR)\")\n\
+	set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)\n\
+	set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)\n\
+	set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)\n\
+	set(ENV{PKG_CONFIG_SYSROOT_DIR} \"$(STAGING_DIR)\")\n\
+	" > $@
 
 .PHONY: all world dirs clean distclean source outputmakefile \
 	$(BASE_TARGETS) $(TARGETS) $(TARGETS_ALL) \

package/Makefile.in

@@ -143,6 +143,14 @@ TARGET_CC  := $(CCACHE) $(TARGET_CC)
 TARGET_CXX := $(CCACHE) $(TARGET_CXX)
 endif
 
+# * CMake doesn't support having the --sysroot option directly in the
+#   compiler path, so move this option to CFLAGS/CXXFLAGS variables.
+# * Don't use ccache because then CMake will fail to detect compiler.
+CMAKE_TARGET_CC = $(filter-out --sysroot=%,$(TARGET_CC_NOCCACHE))
+CMAKE_TARGET_CXX = $(filter-out --sysroot=%,$(TARGET_CXX_NOCCACHE))
+CMAKE_TARGET_CFLAGS = $(filter --sysroot=%,$(TARGET_CC_NOCCACHE)) $(TARGET_CFLAGS)
+CMAKE_TARGET_CXXFLAGS = $(filter --sysroot=%,$(TARGET_CXX_NOCCACHE)) $(TARGET_CXXFLAGS)
+
 ifeq ($(BR2_STRIP_strip),y)
 STRIP_DISCARD_ALL:=--discard-all
 STRIP_STRIP_UNNEEDED:=--strip-unneeded