Activate Fortran interface on demand

Not only if we need to compile Fortran code, but also if we need to call
some functions from a Fortran library from C code.

CMakeLists.txt

@@ -203,12 +203,11 @@ configure_vars (
 	WRITE ${${project}_CONFIG_VARS}
 	)
 
-### --- begin AGMG specific --- ###
 include (UseFortranWrappers)
 define_fc_func (
 	APPEND ${CONFIG_H}
+	IF HAVE_AGMG # HAVE_BLAS HAVE_LAPACK
 	)
-### --- end AGMG specific --- ###
 
 # compile main library; pull in all required includes and libraries
 include (OpmCompile)

cmake/Modules/UseFortranWrappers.cmake

@@ -1,7 +1,7 @@
 # - Provide C wrappers for Fortran code
 #
 # Synopsis:
-#	define_fc_func (APPEND config.h)
+#	define_fc_func (APPEND config.h IF HAVE_BLAS)
 
 function (define_fc_func verb file)
   # check that we are being called correctly
@@ -13,10 +13,40 @@ function (define_fc_func verb file)
   endif (NOT (("${verb}" STREQUAL "APPEND") OR
 		      ("${verb}" STREQUAL "WRITE")))
 
+  # check under which conditions we should do our work
+  if (NOT "${ARGN}" STREQUAL "")
+	set (args ${ARGN})
+	list (GET args 0 keyword)
+	if (NOT "${keyword}" STREQUAL "IF")
+	  message (FATAL_ERROR
+		"Unknown conditional \"${keyword}\" passed as third argument."
+		)
+	endif (NOT "${keyword}" STREQUAL "IF")
+	list (REMOVE_AT args 0)
+	set (needed FALSE)
+	foreach (condition IN LISTS args)
+	  if (${${condition}})
+		set (needed TRUE)
+		break ()
+	  endif (${${condition}})
+	endforeach (condition)
+  else (NOT "${ARGN}" STREQUAL "")
+	# if called unconditionally, then always include the wrapper
+	set (needed TRUE)
+  endif (NOT "${ARGN}" STREQUAL "")
+
   # only do something if we actually have some components which requires
   # the interaction -- don't load the Fortran compiler just to write
   # this macro (which apparently nobody uses then)
-  if (CMAKE_C_COMPILER_LOADED AND CMAKE_Fortran_COMPILER_LOADED)
+  if (needed)
+	# enable languages needed
+	if (NOT CMAKE_C_COMPILER_LOADED)
+	  enable_language (C)
+	endif (NOT CMAKE_C_COMPILER_LOADED)
+	if (NOT CMAKE_Fortran_COMPILER_LOADED)
+	  enable_language (Fortran)
+	endif (NOT CMAKE_Fortran_COMPILER_LOADED)
+
 	# get a temporary file
 	set (_tmp_hdr ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/config_f.h)
 
@@ -42,7 +72,7 @@ function (define_fc_func verb file)
       ${_str}
 	  "\n"
 	  )
-  else (CMAKE_C_COMPILER_LOADED AND CMAKE_Fortran_COMPILER_LOADED)
+  else (needed)
 	message (STATUS "Fortran/C interface not activated")
-  endif (CMAKE_C_COMPILER_LOADED AND CMAKE_Fortran_COMPILER_LOADED)
+  endif (needed)
 endfunction (define_fc_func)