Implement a CMake build for FirebaseAuthInterop (#1532)

* Add a CMake build for FirebaseAuthInterop

* Avoid cluttering the symbol table

* Trigger Firestore-cmake checks on cmake script changes

Author: wilhuff

Firestore/CMakeLists.txt

@@ -144,6 +144,26 @@ podspec_framework(
   ${FIREBASE_SOURCE_DIR}/FirebaseCore.podspec
 )
 
+podspec_framework(
+  ${FIREBASE_SOURCE_DIR}/FirebaseAuthInterop.podspec
+)
+
+# FirebaseAuthInterop has no source files but CMake can't build frameworks that don't
+# have sources. Generate an inconsequential source file so that the library can
+# be linked.
+file(
+  WRITE ${CMAKE_CURRENT_BINARY_DIR}/FirebaseAuthInteropDummy.c
+  "// generated file for header-only CMake support.
+  __attribute__((unused))
+  static void FirebaseAuthInteropFakeSymbol() {}
+  "
+)
+target_sources(
+  FirebaseAuthInterop
+  PRIVATE ${CMAKE_CURRENT_BINARY_DIR}/FirebaseAuthInteropDummy.c
+)
+
+
 # Superbuild installed results
 include_directories(${FIREBASE_INSTALL_DIR}/include)
 

scripts/if_changed.sh

@@ -54,7 +54,7 @@ else
       ;;
 
     Firestore-cmake)
-      check_changes '^Firestore/(core|third_party)'
+      check_changes '^(Firestore/(core|third_party)|cmake)'
       ;;
 
     *)