This will allow the variables [*] to be overridden on a per-PROG basis,
which is useful when controlling "stripping" behavior for some tests
that require debug symbols or to be unstripped
DEBUG_FLAGS (similar to CFLAGS) supports appending, whereas STRIP is
an override
*: Due to how STRIP is defined in bsd.own.mk (in addition to
bsd.lib.mk and bsd.prog.mk), and the fact that bsd.test.mk pulls in
bsd.own.mk first, overriding STRIP doesn't work today.
A follow up commit is pending to "rectify" this after additional
testing is done.
Discussed with: bdrewery
MFC after: 1 week
Sponsored by: EMC / Isilon Storage Division
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