build: add hand-rolled make scaffold (gmake/bmake/build.sh/build.bat)

Static-lib-only build (libfpk.a, no shared/dynamic target), plus a
tools/ build path for fpack/funpack linked against the just-built
static lib. Matches stk's C89 build style; no library source yet.

compile_flags.txt

@@ -0,0 +1,6 @@
+-xc
+-std=c89
+-Wall
+-Wpedantic
+-Iinclude
+