Added error if Fortran's default real is double precision. If it is and HL is being built then configure returns an error. This is due to HDFFV-889.

Tested: jam with intel

cmake options:
-DCMAKE_Fortran_FLAGS:STRING="-r8" (should fail) 
and 
-DHDF5_BUILD_HL_LIB:BOOL=OFF (should pass)