Index: clang/docs/UsersManual.rst
===================================================================
--- clang/docs/UsersManual.rst
+++ clang/docs/UsersManual.rst
@@ -847,6 +847,9 @@
 CLANG_CONFIG_FILE_SYSTEM_DIR respectively. The first file found is used. It is
 an error if the required file cannot be found.
 
+If clang was built with the CMake parameter CLANG_DEFAULT_CONFIG_FILE, and no
+other configuration file is specified, that file is always looked up for.
+
 Another way to specify a configuration file is to encode it in executable name.
 For example, if the Clang executable is named `armv7l-clang` (it may be a
 symbolic link to `clang`), then Clang will search for file `armv7l.cfg` in the
Index: clang/include/clang/Config/config.h.cmake
===================================================================
--- clang/include/clang/Config/config.h.cmake
+++ clang/include/clang/Config/config.h.cmake
@@ -51,6 +51,9 @@
 #cmakedefine CLANG_CONFIG_FILE_SYSTEM_DIR "${CLANG_CONFIG_FILE_SYSTEM_DIR}"
 #cmakedefine CLANG_CONFIG_FILE_USER_DIR "${CLANG_CONFIG_FILE_USER_DIR}"
 
+/* Default config config for clang, prepended to every clang run */
+#cmakedefine CLANG_DEFAULT_CONFIG_FILE "${CLANG_DEFAULT_CONFIG_FILE}"
+
 /* Default <path> to all compiler invocations for --sysroot=<path>. */
 #define DEFAULT_SYSROOT "${DEFAULT_SYSROOT}"
 
Index: clang/lib/Driver/Driver.cpp
===================================================================
--- clang/lib/Driver/Driver.cpp
+++ clang/lib/Driver/Driver.cpp
@@ -871,6 +871,10 @@
         return true;
       }
     }
+#ifdef CLANG_DEFAULT_CONFIG_FILE
+    if (ConfigFiles.empty())
+      ConfigFiles.push_back(CLANG_DEFAULT_CONFIG_FILE);
+#endif
 
     if (!ConfigFiles.empty()) {
       CfgFileName = ConfigFiles.front();