Make Kernel check not mandatory

Use 2 different checks, one specify a mandatory kernel version
and the other will output a warning and position a preprocessing
variable that can be used in the code to exclude portions of code
that use kernel features not available under a certain version.

Bug-AGL: SPEC-772

Change-Id: I04523abe96749aeeb185e90eee154fd70a4cbf19
Signed-off-by: Romain Forlot <romain.forlot@iot.bzh>

# Conflicts:
#	conf.d/app-templates

2 files changed, 12 insertions, 4 deletions

diff --git a/conf.d/app-templates b/conf.d/app-templates
-Subproject 011277d2af3cfee674b50fa8a7362e91e8ad29e
+Subproject ec101c751a6359483a00c0c3923d502845f4512
diff --git a/conf.d/cmake/config.cmake b/conf.d/cmake/config.cmake
index e9ab925b..338b9001 100644
--- a/conf.d/cmake/config.cmake
+++ b/conf.d/cmake/config.cmake
@@ -47,11 +47,19 @@ set(PROJECT_APP_TEMPLATES_DIR "conf.d/app-templates")
 # ----------------------------------
 set(CMAKE_BUILD_TYPE "DEBUG")
 
-# Kernel selection if needed. Impose a minimal version.
-# NOTE FOR NOW IT CHECKS KERNEL Yocto SDK Kernel version
-# else only HOST VERSION
+# Kernel selection if needed. You can choose between a
+# mandatory version to impose a minimal version.
+# Or check Kernel minimal version and just print a Warning
+# about missing features and define a preprocessor variable
+# to be used as preprocessor condition in code to disable
+# incompatibles features. Preprocessor define is named
+# KERNEL_MINIMAL_VERSION_OK.
+#
+# NOTE*** FOR NOW IT CHECKS KERNEL Yocto environment and
+# Yocto SDK Kernel version.
 # -----------------------------------------------
-set (kernel_minimal_version 4.8)
+#set(kernel_mandatory_version 4.8)
+set(kernel_minimal_version 4.8)
 
 # Compiler selection if needed. Impose a minimal version.
 # -----------------------------------------------