Forcibly disable RTCD in CMake mips toolchain files.

- Always force CONFIG_RUNTIME_CPU_DETECT value to 0.
- Warns when user tries to enable CONFIG_RUNTIME_CPU_DETECT.

BUG=aomedia:711

Change-Id: Ic3cad67fc5e5a9ef46ce69838e7eb6bb392df136

build/cmake/toolchains/mips32-linux-gcc.cmake

@@ -66,6 +66,10 @@ set(CMAKE_CXX_COMPILER_ARG1 "-EL ${MIPS_CXXFLAGS}")
 set(CMAKE_SYSTEM_PROCESSOR "mips32")
 
 # No runtime cpu detect for mips32-linux-gcc.
-set(CONFIG_RUNTIME_CPU_DETECT 0 CACHE NUMBER "")
+if (CONFIG_RUNTIME_CPU_DETECT)
+  message("--- CONFIG_RUNTIME_CPU_DETECT not supported for mips32 targets.")
+endif ()
+
+set(CONFIG_RUNTIME_CPU_DETECT 0 CACHE NUMBER "" FORCE)
 
 endif ()  # AOM_BUILD_CMAKE_TOOLCHAINS_MIPS32_LINUX_GCC_CMAKE_

build/cmake/toolchains/mips64-linux-gcc.cmake

@@ -43,6 +43,10 @@ set(CMAKE_CXX_COMPILER_ARG1 "-EL ${MIPS_CXXFLAGS}")
 set(CMAKE_SYSTEM_PROCESSOR "mips64")
 
 # No runtime cpu detect for mips64-linux-gcc.
-set(CONFIG_RUNTIME_CPU_DETECT 0 CACHE NUMBER "")
+if (CONFIG_RUNTIME_CPU_DETECT)
+  message("--- CONFIG_RUNTIME_CPU_DETECT not supported for mips64 targets.")
+endif ()
+
+set(CONFIG_RUNTIME_CPU_DETECT 0 CACHE NUMBER "" FORCE)
 
 endif ()  # AOM_BUILD_CMAKE_TOOLCHAINS_MIPS64_LINUX_GCC_CMAKE_