src/Makefile.am: reinstate empty FCLAW_CPPFLAGS #410

Job	Run time
Automake Serial Minimal Build on Linux	1m 35s
Automake Serial With Clawpack Build on Linux	17m 11s
Automake Serial With GeoClaw Build on Linux	1m 40s
Automake Serial With CudaClaw (CUDA 10.1) Build on Linux	2m 56s
Automake Serial With CudaClaw (CUDA 11.3) Build on Linux	3m 4s
Automake MPI Minimal Build on Linux	2m 8s
Automake MPI Debug With CXX Build on Linux	5m 12s
Automake MPI With Clawpack Build on Linux	16m 52s
Automake MPI With GeoClaw Build on Linux	2m 17s
Automake MPI With CudaClaw (CUDA 10.1) Build on Linux	2m 50s
Automake MPI With CudaClaw (CUDA 11.3) Build on Linux	3m 23s
Automake MPI With ThunderEgg Build on Linux	5m 4s
	1h 4m 12s

Provide feedback