Default to gfortran if cannot figure out F77 compiler

https://bugs.gentoo.org/show_bug.cgi?id=348922

--- netcdf-4.1.1/configure.ac
+++ netcdf-4.1.1/configure.ac
@@ -973,7 +973,7 @@
              *)
                 # If it's a gnu compiler, guess f2c.
                 if test "x$ac_cv_fc_compiler_gnu" = xyes; then
-                   AC_DEFINE(f2cFortran, [1], [Turned on by netCDF configure.])
+                   AC_DEFINE(gFortran, [1], [Turned on by netCDF configure.])
                 fi
                 ;;
          esac