BUILD_MISSING_DEPS - fix minor configuration options

[kaarrot]

Description

Address a few small issues encountered during CMake configuration step and during build using Makefile BUILD_MISSING_DEPS option enabled.

• Mismatch between expected libraw versions specified in build_libraw.bash 0.21.3 and externalpackages.cmake 0.20.0
• OpenEXR link error in libutil tests
• Update top level Makefile to accept BUILD_MISSING_DEPS as string instead of bool. Pass the string option down to CMake

Test

Verified build completes with no errors: BUILD_MISSING_DEPS=all make

[lgritz]

This all looks great, I think the only missing piece is that one or more of your commits lacks the DCO signoff. Maybe the easiest fix is to squash your comments and make sure the one remaining commit has the proper sign-off info?

[kaarrot]

Squashed and signed-off.