[tool] Support additional defines passed to hlc build

[tobil4sk]

This way it is possible to generate hlc code with haxe, and then generate multiple templates from hlc.json.

For example:

haxe --main Main --hl bin/main.c
haxelib run hashlink build bin/main.c -D hlgen.makefile=make
haxelib run hashlink build bin/main.c -D hlgen.makefile=vs2022

This would be useful for example in haxe CI, where we want to test both gcc and msvc hlc builds.