build: Improve value substitution

The waf build system uses lists for tool flags.  The build items may use
variable substitution.  Add the ability to use the variable substitution in
lists.  For example:

MORE_FLAGS = ['-more', '-flags']

flags:
- -some-flag
- ${MORE_FLAGS}

Before this change, the ${MORE_FLAGS} was substituted to "-more -flags".  This
would be passed by waf as a single command line argument to the tool.

After this change, the ${MORE_FLAGS} list extends the flags list:

flags = ['-some-flag', '-more', '-flags']

This list extension is performed if a list element consists of exactly one
variable.

Update #4670.

0 files changed, 0 insertions, 0 deletions