Fix Makefile object names for targets: gfortran, intel-seq

[chstan]

In compiling (initially for Windows and subsequently for Ubuntu with the gfortran toolchain) I ran into this issue where compilation fails because make is treating the targets in a case sensitive way.

I've updated the Makefiles for all targets so they refer to the $(OBJ) with the same case (all caps) as the designated target.

For others in the future, this manifested as an error in the linker because no object files were being built:

gfortran in function _start' (.text+0x20) undefined reference to main'

[codecov-io]

Codecov Report

Merging #65 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #65   +/-   ##
=======================================
  Coverage   31.72%   31.72%           
=======================================
  Files          36       36           
  Lines       13777    13777           
=======================================
  Hits         4371     4371           
  Misses       9406     9406

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