Avoid a semicolon in CMAKE_Fortran_FLAGS when additional flags are passed to cmake

[branfosj]

Name and Institution (Required)

Name: Simon Branford
Institution: University of Birmingham

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Describe the update

This fixes the setting of CMAKE_Fortran_FLAGS in the case where a user wishes to specify additional flags.

In #326 the extra flag was -m64 for me it was -march=native.

git clone https://github.com/geoschem/GCHP.git
cd GCHP
git checkout 14.1.1
git submodule update --init --recursive
mkdir build & cd build
cmake -DCMAKE_Fortran_FLAGS="-march=native" ../
make VERBOSE=1

Expected changes

GCHP to successfully build if there are extra flags passed to cmake via CMAKE_Fortran_FLAGS.

Reference(s)

None

Related Github Issue(s)

#326

[yantosca]

Good to merge

[yantosca]

All GCHP integration tests passed:

==============================================================================
GCHP: Execution Test Results

GCHP      #7b7bfa3 PR #334 post-merge update: Edit CHANGELOG.md
GEOS-Chem #69ae58a1b Merge PR #2069 (Reduce timers to essential list only)
HEMCO     #a5d5169 HEMCO 3.7.2 release

Number of execution tests: 5

Submitted as SLURM job: 12586816
==============================================================================

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%  All execution tests passed!  %%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Also all GCHP integration tests were identical to 14.2.3.