[Libcxx] Add <source_location> header.

This requires the __builtin_source_location() builtin, as implemented
by GCC and Clang.

Fixes https://github.com/llvm/llvm-project/issues/56363

Differential Revision: https://reviews.llvm.org/D120634

NOKEYCHECK=True
GitOrigin-RevId: 73d94b19161355d06f20678d628555719eebbdcc
diff --git a/include/module.modulemap.in b/include/module.modulemap.in
index 8706a46..73bd8a2 100644
--- a/include/module.modulemap.in
+++ b/include/module.modulemap.in
@@ -1291,6 +1291,10 @@
     header "shared_mutex"
     export version
   }
+  module source_location {
+    header "source_location"
+    export *
+  }
   module span {
     header "span"
     export ranges.__ranges.enable_borrowed_range