Merge branch '60-amex-build-18-07_-2-3-d-with-gcc-7-4-0-and-openmpi-3-1-4' into 'master'

Resolve "amex: build 18.07_{2,3}d with gcc/7.4.0 and openmpi/3.1.4"

Closes #60

See merge request Pmodules/buildblocks!74

MPI/amrex/files/variants

@@ -3,6 +3,7 @@ amrex/18.07_2d	unstable	gcc/7.3.0 openmpi/2.1.5 b:cmake/3.9.6
 amrex/18.07_2d	unstable	gcc/7.3.0 openmpi/3.0.0 b:cmake/3.9.6
 amrex/18.07_2d	unstable	gcc/7.3.0 openmpi/3.1.2 b:cmake/3.9.6
 amrex/18.07_2d	unstable	gcc/7.3.0 openmpi/3.1.3 b:cmake/3.9.6
+amrex/18.07_2d	stable		gcc/7.4.0 openmpi/3.1.4 b:cmake/3.10.3
 
 amrex/18.07_2d	unstable	gcc/8.2.0 openmpi/1.10.7 b:cmake/3.9.6
 amrex/18.07_2d	unstable	gcc/8.2.0 openmpi/2.1.5 b:cmake/3.9.6
@@ -17,6 +18,7 @@ amrex/18.07_3d	unstable	gcc/7.3.0 openmpi/2.1.5 b:cmake/3.9.6
 amrex/18.07_3d	unstable	gcc/7.3.0 openmpi/3.0.0 b:cmake/3.9.6
 amrex/18.07_3d	unstable	gcc/7.3.0 openmpi/3.1.2 b:cmake/3.9.6
 amrex/18.07_3d	unstable	gcc/7.3.0 openmpi/3.1.3 b:cmake/3.9.6
+amrex/18.07_3d	stable		gcc/7.4.0 openmpi/3.1.4 b:cmake/3.10.3
 
 amrex/18.07_3d	unstable	gcc/8.2.0 openmpi/1.10.7 b:cmake/3.9.6
 amrex/18.07_3d	unstable	gcc/8.2.0 openmpi/2.1.5 b:cmake/3.9.6