Add Fortran compiler flags for supporting gfortran-10

[climbfuji]

Two items related to this issue:

• Add gfortran-10 compiler flags

 if(${CMAKE_Fortran_COMPILER_ID} MATCHES "^(GNU)$" AND ${CMAKE_Fortran_COMPILER_VERSION} VERSION_GREATER_EQUAL 10)
   set(CMAKE_Fortran_FLAGS "${CMAKE_Fortran_FLAGS} -w -fallow-argument-mismatch -fallow-invalid-boz")
 endif()

• Allow specification of compiler flags from the environment e.g. CFLAGS, FFLAGS

set(CMAKE_Fortran_FLAGS "${CMAKE_Fortran_FLAGS}  existing_fortran_flags")
set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS}  existing_c_flags")

List of libraries that need to be updated:

• [x] bacio
• [x] bufr
• [ ] crtm
• [x] g2
• [x] g2c
• [ ] g2tmpl
• [x] gfsio
• [ ] grib_util
• [x] ip
• [x] ip2
• [x] landsfcutil
• [x] nemsio
• [x] nemsiogfs
• [x] prod_util
• [x] sfcio
• [x] sigio
• [x] sp
• [x] w3emc
• [x] w3nco
• [x] wrf_io

[aerorahul]

This should be done in the repos as well. Not everyone uses the umbrella build. And it is especially not used when installing/updating a single or handful of libraries.

An alternative is to set environment variables.

[kgerheiser]

I'll just go through each library and add it

[aerorahul]

@kgerheiser If you could also add the following:

set(CMAKE_Fortran_FLAGS ${CMAKE_Fortran_FLAGS} ...) 

The above will allow passing FFLAGS from the environment.

Same for CMAKE_C_FLAGS.

We can use this with a list of NCEPLIBS and split the work.