toolchain: cmake: Off-tree toolchains gets other.h included if selected

To ensure that an off-tree toolchain gets the toolchain/other.h header
included, such that it can include the correct header for the
toolchain via the other.h, the define __TOOLCHAIN_CUSTOM__ will be set
when ever the cmake flag TOOLCHAIN_USE_CUSTOM is set.
An off-tree toolchain needs to set the set(TOOLCHAIN_USE_CUSTOM 1) in
the off-tree generic.cmake and/or target.cmake, in order for the
include/other.h to be included. The generic.cmake and target.cmake will
be under ${TOOLCHAIN_ROOT}/cmake/toolchain/${ZEPHYR_TOOLCHAIN_VARIANT}/

As the TOOLCHAIN_USE_CUSTOM is only set for off-tree toolchains, this
has no impact on in-tree toolchains and their functionality.

Fixes #36117

Signed-off-by: Danny Oerndrup <[email protected]>

Author: daor-oti

CMakeLists.txt

@@ -95,6 +95,11 @@ zephyr_compile_definitions(
   __ZEPHYR__=1
 )
 
+# Ensure that include/toolchain.h includes toolchain/other.h for all off-tree toolchains
+if(TOOLCHAIN_USE_CUSTOM)
+  zephyr_compile_definitions(__TOOLCHAIN_CUSTOM__)
+endif()
+
 # @Intent: Set compiler flags to enable buffer overflow checks in libc functions
 # @config in CONFIG_NO_OPTIMIZATIONS optional : Optimizations may affect security
 zephyr_compile_definitions($<TARGET_PROPERTY:compiler,security_fortify> )

include/toolchain.h

@@ -33,7 +33,12 @@
 #define HAS_BUILTIN(x) HAS_BUILTIN_##x
 #endif
 
-#if defined(__XCC__)
+#if defined(__TOOLCHAIN_CUSTOM__)
+/* This include line exists for off-tree definitions of compilers,
+ * and therefore this header is not meant to exist in-tree
+ */
+#include <toolchain/other.h>
+#elif defined(__XCC__)
 #include <toolchain/xcc.h>
 #elif defined(__CCAC__)
 #include <toolchain/mwdt.h>
@@ -42,10 +47,7 @@
 #elif defined(__GNUC__) || (defined(_LINKER) && defined(__GCC_LINKER_CMD__))
 #include <toolchain/gcc.h>
 #else
-/* This include line exists for off-tree definitions of compilers,
- * and therefore this header is not meant to exist in-tree
- */
-#include <toolchain/other.h>
+#error "Invalid/unknown toolchain configuration"
 #endif
 
 /*