BUILD: pass all "USE_*" variables as -DUSE_* to the compiler

BUILD: pass all "USE_*" variables as -DUSE_* to the compiler

Many of these variables are already passed verbatim. Let's now pass
all of them, this will require less changes in the future. A number
of older variables have different names for the makefile and the code
and should be adjusted to further simplify this. A few remain though,
mainly the ones which imply another one (e.g. USE_STATIC_PCRE implies
USE_PCRE).