jom does not set defines based on system calls

jom does not set defines that make external system calls correctly.
1. -DFOO=FOO
2. -DFOO_EXT=$(shell echo FOO_EXT)

1 expands to FOO as expected.
2 expands to nothing.

Sample project attached. Jom output in jom.txt. Mingw32-make output in mingw32-make.txt.