Add wrapper function for setting CMake compiler launcher.

Also adds a missing function doc comment.

Change-Id: I0ff00cb326709134259b0aecc6b60046f209d2a8

build/cmake/aom_configure.cmake

diff --git a/build/cmake/aom_configure.cmake b/build/cmake/aom_configure.cmake
index f306c8c..f7c18d0 100644
--- a/build/cmake/aom_configure.cmake
+++ b/build/cmake/aom_configure.cmake
@@ -149,33 +149,15 @@
 include("${AOM_ROOT}/build/cmake/cpu.cmake")
 
 if (ENABLE_CCACHE)
-  find_program(CCACHE "ccache")
-  if (NOT "${CCACHE}" STREQUAL "")
-    set(CMAKE_C_COMPILER_LAUNCHER "${CCACHE}")
-    set(CMAKE_CXX_COMPILER_LAUNCHER "${CCACHE}")
-  else ()
-    message("--- Cannot find ccache, ENABLE_CCACHE ignored.")
-  endif ()
+  set_compiler_launcher(ENABLE_CCACHE ccache)
 endif ()
 
 if (ENABLE_DISTCC)
-  find_program(DISTCC "distcc")
-  if (NOT "${DISTCC}" STREQUAL "")
-    set(CMAKE_C_COMPILER_LAUNCHER "${DISTCC}")
-    set(CMAKE_CXX_COMPILER_LAUNCHER "${DISTCC}")
-  else ()
-    message("--- Cannot find distcc, ENABLE_DISTCC ignored.")
-  endif ()
+  set_compiler_launcher(ENABLE_DISTCC distcc)
 endif ()
 
 if (ENABLE_GOMA)
-  find_program(GOMACC "gomacc")
-  if (NOT "${GOMACC}" STREQUAL "")
-    set(CMAKE_C_COMPILER_LAUNCHER "${GOMACC}")
-    set(CMAKE_CXX_COMPILER_LAUNCHER "${GOMACC}")
-  else ()
-    message("--- Cannot find gomacc, ENABLE_GOMA ignored.")
-  endif ()
+  set_compiler_launcher(ENABLE_GOMA gomacc)
 endif ()
 
 if (NOT CONFIG_AV1_DECODER AND NOT CONFIG_AV1_ENCODER)

build/cmake/util.cmake

diff --git a/build/cmake/util.cmake b/build/cmake/util.cmake
index 7d2b6c0..786e342 100644
--- a/build/cmake/util.cmake
+++ b/build/cmake/util.cmake
@@ -24,6 +24,8 @@
   set(${out_file_path} ${dummy_source_file} PARENT_SCOPE)
 endfunction ()
 
+# Convenience function for adding a dummy source file to $target_name using
+# $extension as the file extension. Wraps create_dummy_source_file().
 function (add_dummy_source_file_to_target target_name extension)
   create_dummy_source_file("${target_name}" "${extension}" "dummy_source_file")
   target_sources(${target_name} PRIVATE ${dummy_source_file})
@@ -45,5 +47,20 @@
   message(WARNING "--- ${warning_message}")
 endfunction ()
 
+# Sets CMake compiler launcher to $launcher_name when $launcher_name is found in
+# $PATH. Warns user about ignoring build flag $launcher_flag when $launcher_name
+# is not found in $PATH.
+function (set_compiler_launcher launcher_flag launcher_name)
+  find_program(launcher_path "${launcher_name}")
+  if (launcher_path)
+    set(CMAKE_C_COMPILER_LAUNCHER "${launcher_path}" PARENT_SCOPE)
+    set(CMAKE_CXX_COMPILER_LAUNCHER "${launcher_path}" PARENT_SCOPE)
+    message("--- Using ${launcher_name} as compiler launcher.")
+  else ()
+    message(WARNING
+            "--- Cannot find ${launcher_name}, ${launcher_flag} ignored.")
+  endif ()
+endfunction ()
+
 endif()  # AOM_BUILD_CMAKE_UTIL_CMAKE_