[source] cmake: skip build system check on compile

[LEDE Commits]

nbd pushed a commit to source.git, branch lede-17.01:
https://git.lede-project.org/f6d94b0dd67f4d5e5dbadbd97a765732d6a0e757

commit f6d94b0dd67f4d5e5dbadbd97a765732d6a0e757
Author: Felix Fietkau <nbd at nbd.name>
AuthorDate: Mon Feb 20 12:13:51 2017 +0100

    cmake: skip build system check on compile
    
    cmake checks the build system and its variables on its own to detect if
    the makefiles need to be regenerated.
    Unfortunately this can invalidate overrides passed in the
    Build/Configure step. On non-Linux systems this breaks the build when
    switching between targets of the same package architecture.
    
    Fix this by forcibly disabling the build system check and relying on the
    LEDE build system to take care of these things
    
    Signed-off-by: Felix Fietkau <nbd at nbd.name>
---
 include/cmake.mk | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/cmake.mk b/include/cmake.mk
index 5f572e9..5a403cb 100644
--- a/include/cmake.mk
+++ b/include/cmake.mk
@@ -107,3 +107,7 @@ define Host/Configure/Default
 		$(HOST_CMAKE_SOURCE_DIR) \
 	)
 endef
+
+MAKE_FLAGS += \
+	CMAKE_COMMAND='$$(if $$(CMAKE_DISABLE_$$@),:,$(STAGING_DIR_HOST)/bin/cmake)' \
+	CMAKE_DISABLE_cmake_check_build_system=1