[Buildroot] [PATCH 1/2] toolchainfile.cmake: force setting CMAKE_{C, CXX, LINKER}_FLAGS

[Samuel Martin <s.martin49@gmail.com>]

According to the build configuration, Buildroot defines some
compiler/linker flags.

For CMake packages, these flags are passed thanks to the
toolchainfile.cmake file, which is filled by Buildroot.

The toolchainfile.cmake should make sure the flags preset by Buildroot
are correctly passed to the compiler, while it should also allow passing
per-package flags using the standard CMake variables for this.

This is achieved using the 'set' CMake command to extend the standard
CMAKE_{C,CXX,LINKER}_FLAGS variables.
However, we have to be careful with the option passed to the 'set'
command [1] to make sure even these cache entry will be
extended/overwritten; otherwise the preset value will take precedence
(the per-package flags in Buildroot case) and the variable will not be
extended.

So, this change makes sure the toolchainfile.camke file will actually
extend/overwrite the compiler and linker flags with the Buildroot's
predefined flags.

[1] https://cmake.org/cmake/help/v3.6/command/set.html

Fixes:
  http://autobuild.buildroot.net/results/7f1c96abd8fbb5b358a07100ab623316e9bb9dcd
  http://autobuild.buildroot.net/results/e0c93d0f6d1da0d62d4dbba211a275bfe75e9645
  http://autobuild.buildroot.net/results/53e7e4b4b6a7b48b8012799d7507f7594dbf01b2

Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
---
 support/misc/toolchainfile.cmake.in | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/support/misc/toolchainfile.cmake.in b/support/misc/toolchainfile.cmake.in
index 649b52d..eddea56 100644
--- a/support/misc/toolchainfile.cmake.in
+++ b/support/misc/toolchainfile.cmake.in
@@ -13,9 +13,9 @@ string(REPLACE "/usr/share/buildroot" "" RELOCATED_HOST_DIR ${CMAKE_CURRENT_LIST
 set(CMAKE_SYSTEM_NAME Linux)
 set(CMAKE_SYSTEM_PROCESSOR @@CMAKE_SYSTEM_PROCESSOR@@)
 
-set(CMAKE_C_FLAGS "@@TARGET_CFLAGS@@ ${CMAKE_C_FLAGS}" CACHE STRING "Buildroot CFLAGS")
-set(CMAKE_CXX_FLAGS "@@TARGET_CXXFLAGS@@ ${CMAKE_CXX_FLAGS}" CACHE STRING "Buildroot CXXFLAGS")
-set(CMAKE_EXE_LINKER_FLAGS "@@TARGET_LDFLAGS@@ ${CMAKE_EXE_LINKER_FLAGS}" CACHE STRING "Buildroot LDFLAGS")
+set(CMAKE_C_FLAGS "@@TARGET_CFLAGS@@ ${CMAKE_C_FLAGS}" CACHE STRING "Buildroot CFLAGS" FORCE)
+set(CMAKE_CXX_FLAGS "@@TARGET_CXXFLAGS@@ ${CMAKE_CXX_FLAGS}" CACHE STRING "Buildroot CXXFLAGS" FORCE)
+set(CMAKE_EXE_LINKER_FLAGS "@@TARGET_LDFLAGS@@ ${CMAKE_EXE_LINKER_FLAGS}" CACHE STRING "Buildroot LDFLAGS" FORCE)
 set(CMAKE_INSTALL_SO_NO_EXE 0)
 
 set(CMAKE_PROGRAM_PATH "${RELOCATED_HOST_DIR}/usr/bin")
@@ -31,6 +31,6 @@ set(ENV{PKG_CONFIG_SYSROOT_DIR} "${RELOCATED_HOST_DIR}/@@STAGING_SUBDIR@@")
 set(CMAKE_C_COMPILER "${RELOCATED_HOST_DIR}/@@TARGET_CC@@")
 set(CMAKE_CXX_COMPILER "${RELOCATED_HOST_DIR}/@@TARGET_CXX@@")
 if(@@TOOLCHAIN_HAS_FORTRAN@@)
-  set(CMAKE_Fortran_FLAGS "@@TARGET_FCFLAGS@@ ${CMAKE_Fortran_FLAGS}" CACHE STRING "Buildroot FCFLAGS")
+  set(CMAKE_Fortran_FLAGS "@@TARGET_FCFLAGS@@ ${CMAKE_Fortran_FLAGS}" CACHE STRING "Buildroot FCFLAGS" FORCE)
   set(CMAKE_Fortran_COMPILER "${RELOCATED_HOST_DIR}/@@TARGET_FC@@")
 endif()
-- 
2.10.0