Add -foc-intrinsic-path to let the use specify a custom location for

clang's intrinsic headers. This path is relative to clang's binary dir
(which can be set with -foc-compiler-path)

wrapper/main.cpp

@@ -172,6 +172,11 @@ bool compilerpath(Target &target, const char *, const char *path, char **) {
   return true;
 }
 
+bool intrinsicpath(Target &target, const char *, const char *path, char **) {
+  target.intrinsicpath = path;
+  return true;
+}
+
 bool runprog(Target &target, const char *, const char *progname, char **cargs) {
   auto *prog = program::getprog(progname);
 
@@ -263,7 +268,13 @@ constexpr struct Opt {
   {"-icxx-isystem", checkincludepath, true, true},
   {"-cxx-isystem", checkincludepath, true, true},
   {"-I", checkincludepath, true, true},
-  {"-foc-compiler-path", compilerpath, true, false, "="} // sets a custom path for the compiler
+
+  // sets a custom path for the compiler
+  {"-foc-compiler-path", compilerpath, true, false, "="},
+
+  // specifies an additional directory to search when looking for clang's
+  // intrinsic paths
+  {"-foc-intrinsic-path", intrinsicpath, true, false, "="}
 };
 
 bool parse(int argc, char **argv, Target &target) {

wrapper/target.cpp

@@ -409,6 +409,10 @@ do {                                                                           \
   TRYDIR2("/../include/clang");
   TRYDIR2("/usr/include/clang");
 
+  if (!intrinsicpath.empty()) {
+    TRYDIR2(intrinsicpath);
+  }
+
   return false;
 #undef TRYDIR
 #undef TRYDIR2

wrapper/target.h

@@ -149,6 +149,7 @@ struct Target {
   string_vector args;
   const char *language;
   char execpath[PATH_MAX + 1];
+  std::string intrinsicpath;
 };
 
 } // namespace target