#84 Fix parallel build in lib/Makefile

[Sergei Trofimovich]

Without the change there is no guarantee that .o files will be built
after directories are created for them and build fails as:

gcc -I/build/gnu-efi-code//lib ... -c lib/runtime/rtstr.c -o runtime/rtstr.o
Assembler messages:
Fatal error: can't create runtime/rtstr.o: No such file or directory

Build failures are triggered best with make --shuffle mode added to GNU make recently: https://savannah.gnu.org/bugs/index.php?62100

[Nigel Croxon]

Patch is accepted and merged
Thank you for the patch.

commit 2ed6486834634130fe7bc9b8803b0113767fc7c1 (HEAD -> master)
Author: Sergei Trofimovich slyich@gmail.com
Date: Wed Jun 22 23:00:44 2022 +0100

lib/Makefile: add .o file dependency on libsubdirs targets