Find{BLAS,LAPACK}: Fix when used in pure Fortran projects (#16039)

Use `CMAKE_<LANG>_COMPILER_LOADED` to detect enabled languages because
`if( _LANGUAGES_ MATCHES C )` is always true on Windows as the RC
language is activated automatically and matches C.

Modules/FindBLAS.cmake

@@ -59,12 +59,7 @@ set(CMAKE_REQUIRED_QUIET ${BLAS_FIND_QUIETLY})
 set(_blas_ORIG_CMAKE_FIND_LIBRARY_SUFFIXES ${CMAKE_FIND_LIBRARY_SUFFIXES})
 
 # Check the language being used
-get_property( _LANGUAGES_ GLOBAL PROPERTY ENABLED_LANGUAGES )
-if( _LANGUAGES_ MATCHES Fortran )
-  set( _CHECK_FORTRAN TRUE )
-elseif( (_LANGUAGES_ MATCHES C) OR (_LANGUAGES_ MATCHES CXX) )
-  set( _CHECK_FORTRAN FALSE )
-else()
+if( NOT (CMAKE_C_COMPILER_LOADED OR CMAKE_CXX_COMPILER_LOADED OR CMAKE_Fortran_COMPILER_LOADED) )
   if(BLAS_FIND_REQUIRED)
     message(FATAL_ERROR "FindBLAS requires Fortran, C, or C++ to be enabled.")
   else()
@@ -132,7 +127,7 @@ if(_libraries_work)
   # Test this combination of libraries.
   set(CMAKE_REQUIRED_LIBRARIES ${_flags} ${${LIBRARIES}} ${_thread})
 #  message("DEBUG: CMAKE_REQUIRED_LIBRARIES = ${CMAKE_REQUIRED_LIBRARIES}")
-  if (_CHECK_FORTRAN)
+  if (CMAKE_Fortran_COMPILER_LOADED)
     check_fortran_function_exists("${_name}" ${_prefix}${_combined_name}_WORKS)
   else()
     check_function_exists("${_name}_" ${_prefix}${_combined_name}_WORKS)
@@ -483,7 +478,7 @@ if (BLA_VENDOR MATCHES "Intel" OR BLA_VENDOR STREQUAL "All")
  if (NOT WIN32)
   set(LM "-lm")
  endif ()
- if (_LANGUAGES_ MATCHES C OR _LANGUAGES_ MATCHES CXX)
+ if (CMAKE_C_COMPILER_LOADED OR CMAKE_CXX_COMPILER_LOADED)
   if(BLAS_FIND_QUIETLY OR NOT BLAS_FIND_REQUIRED)
     find_package(Threads)
   else()

Modules/FindLAPACK.cmake

@@ -48,11 +48,20 @@
 
 set(_lapack_ORIG_CMAKE_FIND_LIBRARY_SUFFIXES ${CMAKE_FIND_LIBRARY_SUFFIXES})
 
-get_property(_LANGUAGES_ GLOBAL PROPERTY ENABLED_LANGUAGES)
-if (NOT _LANGUAGES_ MATCHES Fortran)
-include(${CMAKE_CURRENT_LIST_DIR}/CheckFunctionExists.cmake)
-else ()
+# Check the language being used
+if( NOT (CMAKE_C_COMPILER_LOADED OR CMAKE_CXX_COMPILER_LOADED OR CMAKE_Fortran_COMPILER_LOADED) )
+  if(LAPACK_FIND_REQUIRED)
+    message(FATAL_ERROR "FindLAPACK requires Fortran, C, or C++ to be enabled.")
+  else()
+    message(STATUS "Looking for LAPACK... - NOT found (Unsupported languages)")
+    return()
+  endif()
+endif()
+
+if (CMAKE_Fortran_COMPILER_LOADED)
 include(${CMAKE_CURRENT_LIST_DIR}/CheckFortranFunctionExists.cmake)
+else ()
+include(${CMAKE_CURRENT_LIST_DIR}/CheckFunctionExists.cmake)
 endif ()
 include(${CMAKE_CURRENT_LIST_DIR}/CMakePushCheckState.cmake)
 
@@ -125,7 +134,7 @@ if(_libraries_work)
     set(CMAKE_REQUIRED_LIBRARIES ${_flags} ${${LIBRARIES}} ${_blas} ${_threads})
   endif()
 #  message("DEBUG: CMAKE_REQUIRED_LIBRARIES = ${CMAKE_REQUIRED_LIBRARIES}")
-  if (NOT _LANGUAGES_ MATCHES Fortran)
+  if (NOT CMAKE_Fortran_COMPILER_LOADED)
     check_function_exists("${_name}_" ${_prefix}${_combined_name}_WORKS)
   else ()
     check_fortran_function_exists(${_name} ${_prefix}${_combined_name}_WORKS)
@@ -250,7 +259,7 @@ if (BLA_VENDOR MATCHES "Intel" OR BLA_VENDOR STREQUAL "All")
   if (NOT WIN32)
     set(LM "-lm")
   endif ()
-  if (_LANGUAGES_ MATCHES C OR _LANGUAGES_ MATCHES CXX)
+  if (CMAKE_C_COMPILER_LOADED OR CMAKE_CXX_COMPILER_LOADED)
     if(LAPACK_FIND_QUIETLY OR NOT LAPACK_FIND_REQUIRED)
       find_PACKAGE(Threads)
     else()