Xcode: Add frameworks search paths from link dependeny closure (#13397)

The Xcode generator produces FRAMEWORK_SEARCH_PATHS from:

(1) Include directories of the form /path/to/Foo.framework become
    -F/path/to so '#include <Foo/H>' can find H in the framework.

(2) Linked frameworks of the form /path/to/Foo.framework become
    -F/path/to -framework Foo so the linker can find the framework.

Originally commit 82bb6fae (add framework support to FIND_FILE,
2005-12-27) added these and used the (then current) old-style link
dependency analysis results to get the frameworks.  Later a second
setting was added by commit 2ed6191f (add initial xcode framework stuff,
2007-05-08) to transform -F/path/to linker options produced by the old
link line generation into entries appended to FRAMEWORK_SEARCH_PATHS.
Then commit 96fd5909 (Implement linking with paths to library files,
2008-01-22) updated the second setting to directly use the results of
full modern link dependency analysis, but forgot to remove the use of
old-style link results from the original setting location.

The two settings worked together for a while, with the second one
appending to the first.  Then commit f33a27ab (Generate native Xcode 3.0
and 3.1 projects, 2009-06-29) changed the internal representation format
produced by the first setting but did not update the second setting to
append to the new representation.  As a result, if the first setting
added any paths (usually via the old-style link analysis) then the
second setting containing the modern link analysis results would not be
applied at all.

Fix this by removing use of the old-style link analysis results.
Replace it using the modern link dependencies and remove the second
setting altogether.  Now all values for FRAMEWORK_SEARCH_PATHS are
collected in one place so no special append logic is needed.