Cannot build individual executables with Makefile

I have a script which requires only the `woff2_compress` and `woff_decompress` executables to be built, so I would like to build just those targets with `make`. However, the Makefile seems to bundle all of the dependencies together, and I end up with an error like this:

```
$ make woff2_compress woff2_decompress
g++ -fno-omit-frame-pointer -no-canonical-prefixes -DFONT_COMPRESSION_BIN -D __STDC_FORMAT_MACROS -fno-tree-vrp -std=c++11 -I./brotli/c/include/ -I./src -I./include -c -o src/woff2_compress.o src/woff2_compress.cc
...more stuff...
make[1]: Leaving directory '/home/bdusell/Programming/github/webfont-generator/vendor/woff2/brotli'
g++ src/font.o src/glyph.o src/normalize.o src/table_tags.o src/transform.o src/woff2_dec.o src/woff2_enc.o src/woff2_common.o src/woff2_out.o src/variable_length.o brotli/bin/obj/c/common/*.o brotli/bin/obj/c/enc/*.o brotli/bin/obj/c/dec/*.o src/woff2_compress.o -o woff2_compress
g++: error: src/font.o: No such file or directory
g++: error: src/glyph.o: No such file or directory
g++: error: src/normalize.o: No such file or directory
g++: error: src/table_tags.o: No such file or directory
g++: error: src/transform.o: No such file or directory
g++: error: src/woff2_dec.o: No such file or directory
g++: error: src/woff2_enc.o: No such file or directory
g++: error: src/woff2_common.o: No such file or directory
g++: error: src/woff2_out.o: No such file or directory
g++: error: src/variable_length.o: No such file or directory
Makefile:56: recipe for target 'woff2_compress' failed
make: *** [woff2_compress] Error 1
```

I would prefer to avoid requiring the user to install CMake.