cmake/compiler/gcc: Fall back to host compiler for x86_64

If we don't have a detected cross compiler for x86_64, use the host
compiler instead.

Signed-off-by: Andy Ross <[email protected]>

Author: Andy Ross

cmake/compiler/gcc/target.cmake

@@ -14,6 +14,29 @@ find_program(CMAKE_READELF    ${CROSS_COMPILE}readelf PATH ${TOOLCHAIN_HOME} NO_
 find_program(CMAKE_GDB        ${CROSS_COMPILE}gdb     PATH ${TOOLCHAIN_HOME} NO_DEFAULT_PATH)
 find_program(CMAKE_NM         ${CROSS_COMPILE}nm      PATH ${TOOLCHAIN_HOME} NO_DEFAULT_PATH)
 
+# x86_64 should pick up a proper cross compiler if one is provided,
+# but falling back to using the host toolchain is a very sane behavior
+# too.
+if(CONFIG_X86_64)
+  if(CMAKE_C_COMPILER STREQUAL CMAKE_C_COMPILER-NOTFOUND)
+    find_program(CMAKE_C_COMPILER   gcc    )
+    find_program(CMAKE_OBJCOPY      objcopy)
+    find_program(CMAKE_OBJDUMP      objdump)
+    find_program(CMAKE_AR           ar     )
+    find_program(CMAKE_RANLILB      ranlib )
+    find_program(CMAKE_READELF      readelf)
+    find_program(CMAKE_GDB          gdb    )
+  endif()
+
+  # When building in x32 mode with a host compiler, there is no libgcc
+  # shipped (because it's an x86_64 compiler, not x32).  That's
+  # actually non-fatal, as no known features we hit in existing code
+  # actually require the library.  But I can't find an exaustive list
+  # of exactly what can break, so this is fragile.  Long term we
+  # really need to be blessing a proper cross toolchain.
+  set(no_libgcc Y)
+endif()
+
 if(CONFIG_CPLUSPLUS)
   set(cplusplus_compiler ${CROSS_COMPILE}${C++})
 else()