Generalize target/prerequisite var block, initial ad hoc target work

Target/prerequisite-specific variable blocks can now be present even if
there are prerequisites. For example, now instead of:

exe{foo}: cxx{foo}
exe{foo}: cc.loptions += ...

Or:

exe{foo}: cxx{foo}
exe{foo}:
{
  cc.loptions += ...
  cc.libs += ...
}

We can write:

exe{foo}: cxx{foo}
{
  cc.loptions += ...
  cc.libs += ...
}

This also works with dependency chains in which case the block applies
to the set of prerequisites (note: not targets) before the last ':'. For
example:

./: exe{foo}: libue{foo}: cxx{foo}
{
  bin.whole = false  # Applies to the libue{foo} prerequisite.
}

0 files changed, 0 insertions, 0 deletions