Add cmake utility functions for setting C/CXX/AS/LD flags.

BUG=https://bugs.chromium.org/p/aomedia/issues/detail?id=76

Change-Id: I495d50eec653d67e44929a8317e308e9c9570e00

build/cmake/aom_optimization.cmake

@@ -119,7 +119,8 @@ function (add_asm_library lib_name asm_sources dependent_target)
     set(asm_object "${asm_lib_obj_dir}/${asm_source_name}.o")
     add_custom_command(OUTPUT "${asm_object}"
                        COMMAND ${YASM_EXECUTABLE}
-                       ARGS -f ${objformat}
+                       ARGS ${AOM_AS_FLAGS}
+                            -f ${objformat}
                             -I${AOM_ROOT} -I${AOM_CONFIG_DIR}
                             -o "${asm_object}" "${asm_source}"
                        DEPENDS "${asm_source}"

build/cmake/compiler_flags.cmake

@@ -171,3 +171,50 @@ function (add_preproc_definition preproc_def)
   add_c_preproc_definition(${preproc_def})
   add_cxx_preproc_definition(${preproc_def})
 endfunction ()
+
+# Adds $flag to assembler command line.
+function (append_as_flag flag)
+  unset(AS_FLAG_FOUND CACHE)
+  string(FIND "${AOM_AS_FLAGS}" "${flag}" AS_FLAG_FOUND)
+
+  if (${AS_FLAG_FOUND} EQUAL -1)
+    set(AOM_AS_FLAGS "${AOM_AS_FLAGS} ${flag}" CACHE STRING "" FORCE)
+  endif ()
+endfunction ()
+
+# Adds $flag to the C compiler command line.
+function (append_c_flag flag)
+  unset(C_FLAG_FOUND CACHE)
+  string(FIND "${CMAKE_C_FLAGS}" "${flag}" C_FLAG_FOUND)
+
+  if (${C_FLAG_FOUND} EQUAL -1)
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${flag}" CACHE STRING "" FORCE)
+  endif ()
+endfunction ()
+
+# Adds $flag to the CXX compiler command line.
+function (append_cxx_flag flag)
+  unset(CXX_FLAG_FOUND CACHE)
+  string(FIND "${CMAKE_CXX_FLAGS}" "${flag}" CXX_FLAG_FOUND)
+
+  if (${CXX_FLAG_FOUND} EQUAL -1)
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${flag}" CACHE STRING "" FORCE)
+  endif ()
+endfunction ()
+
+# Adds $flag to the C and CXX compiler command lines.
+function (append_compiler_flag flag)
+  append_c_flag(${flag})
+  append_cxx_flag(${flag})
+endfunction ()
+
+# Adds $flag to the executable linker command line.
+function (append_exe_linker_flag flag)
+  unset(LINKER_FLAG_FOUND CACHE)
+  string(FIND "${CMAKE_EXE_LINKER_FLAGS}" "${flag}" LINKER_FLAG_FOUND)
+
+  if (${LINKER_FLAG_FOUND} EQUAL -1)
+    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${flag}" CACHE STRING
+        "" FORCE)
+  endif ()
+endfunction ()