Adding ability to specify the libMesh pkconfig type with the METHOD env var.

Author: pshriwise

cmake/Modules/FindLIBMESH.cmake

@@ -5,13 +5,16 @@ if(${CMAKE_VERSION} VERSION_LESS 3.12.0)
     message(FATAL_ERROR "OpenMC builds with libMesh support require CMake version 3.12.0 or greater.")
 endif()
 
+set(LIBMESH_PC_FILE libmesh)
+
+# if the METHOD variable is present, check specifically for
+# the libMesh .pc file for that build type
+if(DEFINED ENV{METHOD})
+  set(LIBMESH_PC_FILE libmesh-$ENV{METHOD})
+  message(STATUS "Using environment variable METHOD to determine libMesh build: ${LIBMESH_PC_FILE}")
+endif()
+
 include(FindPkgConfig)
 set(ENV{PKG_CONFIG_PATH} "$ENV{PKG_CONFIG_PATH}:${LIBMESH_PC}")
 set(PKG_CONFIG_USE_CMAKE_PREFIX_PATH True)
-pkg_check_modules(LIBMESH REQUIRED libmesh>=1.6.0 IMPORTED_TARGET)
-
-find_path(LIBMESH_PC NAMES libmesh.pc
-          HINTS ${LIBMESH_LIBDIR}
-          PATHS ENV LD_LIBRARY_PATH
-          PATH_SUFFIXES lib/pkgconfig pkgconfig
-          NO_DEFAULT_PATH)
+pkg_check_modules(LIBMESH REQUIRED ${LIBMESH_PC_FILE}>=1.6.0 IMPORTED_TARGET)