Use WITH_TIDY_FLAGS env variable.

This variable is a space separated string of clang-tidy flags to be passed
to clang-tidy before any other system required extra flags.
Note that when this flag or local tidy_flags is defined,
the default -header-filter flag is suppressed.

Test: make with WITH_TIDY=1 WITH_TIDY_FLAGS="-extra-arg=-DABCD1=1 -extra-arg=-DABCD2=2"
Bug: 32668284
Change-Id: If7bd31c65404ef7fe6c3499d51f0f209a704efd9