Fix CXX/Fortran MODULE flags when enabled before C (#12929)

If CXX or Fortran is enabled before C then the values of

  CMAKE_SHARED_MODULE_C_FLAGS
  CMAKE_SHARED_MODULE_CREATE_C_FLAGS

may not be available.  On platforms where MODULE library (plugin) creation
is the same as SHARED library creation initialize the MODULE creation
flags from the SHARED creation flags of the matching language instead of
assuming that C has been enabled first.

Teach the COnly and CxxOnly tests to build MODULE libraries.  The latter
covers this specific case.

Modules/CMakeCXXInformation.cmake

@@ -93,12 +93,6 @@ IF(CMAKE_USER_MAKE_RULES_OVERRIDE_CXX)
 ENDIF()
 
 
-# for most systems a module is the same as a shared library
-# so unless the variable CMAKE_MODULE_EXISTS is set just
-# copy the values from the LIBRARY variables
-IF(NOT CMAKE_MODULE_EXISTS)
-  SET(CMAKE_SHARED_MODULE_CXX_FLAGS ${CMAKE_SHARED_LIBRARY_CXX_FLAGS})
-ENDIF(NOT CMAKE_MODULE_EXISTS)
 # Create a set of shared library variable specific to C++
 # For 90% of the systems, these are the same flags as the C versions
 # so if these are not set just copy the flags from the c version
@@ -158,6 +152,14 @@ IF(NOT CMAKE_INCLUDE_FLAG_SEP_CXX)
   SET(CMAKE_INCLUDE_FLAG_SEP_CXX ${CMAKE_INCLUDE_FLAG_SEP_C})
 ENDIF(NOT CMAKE_INCLUDE_FLAG_SEP_CXX)
 
+# for most systems a module is the same as a shared library
+# so unless the variable CMAKE_MODULE_EXISTS is set just
+# copy the values from the LIBRARY variables
+IF(NOT CMAKE_MODULE_EXISTS)
+  SET(CMAKE_SHARED_MODULE_CXX_FLAGS ${CMAKE_SHARED_LIBRARY_CXX_FLAGS})
+  SET(CMAKE_SHARED_MODULE_CREATE_CXX_FLAGS ${CMAKE_SHARED_LIBRARY_CREATE_CXX_FLAGS})
+ENDIF(NOT CMAKE_MODULE_EXISTS)
+
 # repeat for modules
 IF(NOT CMAKE_SHARED_MODULE_CREATE_CXX_FLAGS)
   SET(CMAKE_SHARED_MODULE_CREATE_CXX_FLAGS ${CMAKE_SHARED_MODULE_CREATE_C_FLAGS})

Modules/CMakeFortranInformation.cmake

@@ -109,6 +109,14 @@ IF(NOT DEFINED CMAKE_SHARED_LIBRARY_SONAME_Fortran_FLAG)
   SET(CMAKE_SHARED_LIBRARY_SONAME_Fortran_FLAG ${CMAKE_SHARED_LIBRARY_SONAME_C_FLAG})
 ENDIF()
 
+# for most systems a module is the same as a shared library
+# so unless the variable CMAKE_MODULE_EXISTS is set just
+# copy the values from the LIBRARY variables
+IF(NOT CMAKE_MODULE_EXISTS)
+  SET(CMAKE_SHARED_MODULE_Fortran_FLAGS ${CMAKE_SHARED_LIBRARY_Fortran_FLAGS})
+  SET(CMAKE_SHARED_MODULE_CREATE_Fortran_FLAGS ${CMAKE_SHARED_LIBRARY_CREATE_Fortran_FLAGS})
+ENDIF(NOT CMAKE_MODULE_EXISTS)
+
 # repeat for modules
 IF(NOT DEFINED CMAKE_SHARED_MODULE_CREATE_Fortran_FLAGS)
   SET(CMAKE_SHARED_MODULE_CREATE_Fortran_FLAGS ${CMAKE_SHARED_MODULE_CREATE_C_FLAGS})

Tests/COnly/CMakeLists.txt

@@ -19,3 +19,5 @@ if("${LANG}" STREQUAL "C")
 else("${LANG}" STREQUAL "C")
   message(FATAL_ERROR "Bad language for file conly.c")
 endif("${LANG}" STREQUAL "C")
+
+add_library(testCModule MODULE testCModule.c)

Tests/COnly/testCModule.c

@@ -0,0 +1,6 @@
+#ifdef _WIN32
+# define TEST_EXPORT __declspec(dllexport)
+#else
+# define TEST_EXPORT
+#endif
+TEST_EXPORT int testCModule(void) { return 0; }

Tests/CxxOnly/CMakeLists.txt

@@ -9,3 +9,5 @@ add_library(testcxx1.my STATIC libcxx1.cxx ${EXTRA_SRCS})
 add_library(testcxx2 SHARED libcxx2.cxx)
 add_executable (CxxOnly cxxonly.cxx)
 target_link_libraries(CxxOnly testcxx1.my testcxx2)
+
+add_library(testCxxModule MODULE testCxxModule.cxx)

Tests/CxxOnly/testCxxModule.cxx

@@ -0,0 +1,6 @@
+#ifdef _WIN32
+# define TEST_EXPORT __declspec(dllexport)
+#else
+# define TEST_EXPORT
+#endif
+TEST_EXPORT int testCxxModule(void) { return 0; }