Add C compiler on Hercules to fix ParMetis issue

cmake/SCHISM.local.hercules

@@ -1,10 +1,10 @@
 ###MSU Hercules
-###ParMETIS not working due to icc
 
 set (SCHISM_EXE_BASENAME pschism_HERCULES CACHE STRING "Base name (modules and file extension to be added of the executable. If you want a machine name, add it here")
 
 ###Relative paths won't work
 set(CMAKE_Fortran_COMPILER ifort CACHE PATH "Path to serial Fortran compiler")
+set(CMAKE_C_COMPILER icc CACHE PATH "Path to serial C compiler")
 set(NetCDF_FORTRAN_DIR "$ENV{NETCDF_FORTRAN_ROOT}" CACHE PATH "Path to NetCDF Fortran library")
 set(NetCDF_C_DIR  "$ENV{NETCDF_C_ROOT}"  CACHE PATH "Path to NetCDF C library")