[nrf temphack] trusted-firmware-m: Use find_program for C compiler

Otherwise, the build can't find the compiler executable on Windows

Ref: NCSDK-8303

Signed-off-by: Øyvind Rønningstad <[email protected]>

Author: oyvindronningstad

trusted-firmware-m/toolchain_GNUARM.cmake

@@ -13,8 +13,13 @@ endif()
 
 set(CMAKE_SYSTEM_NAME Generic)
 
-set(CMAKE_C_COMPILER ${CROSS_COMPILE}-gcc)
-set(CMAKE_ASM_COMPILER ${CROSS_COMPILE}-gcc)
+find_program(CMAKE_C_COMPILER ${CROSS_COMPILE}-gcc)
+
+if(CMAKE_C_COMPILER STREQUAL "CMAKE_C_COMPILER-NOTFOUND")
+    message(FATAL_ERROR "Could not find compiler: '${CROSS_COMPILE}-gcc'")
+endif()
+
+set(CMAKE_ASM_COMPILER ${CMAKE_C_COMPILER})
 
 set(LINKER_VENEER_OUTPUT_FLAG -Wl,--cmse-implib,--out-implib=)
 set(COMPILER_CMSE_FLAG -mcmse)