[Fuchsia] Only build symbol archives in Official builds.

Symbol archives are only really useful for Official builds, to enable
crash stacks generated on devies to by symbolized offline.  Splitting
the symbols out of binaries and compression them takes an extremely
long time for high |symbol_level|s, and is not parallelized in our
current implementation.  This makes Debug 'all' builds very slow.

Switch the symbol_archive() targets to be defined only in Official
builds, since that is the only configuration in which we archive them.

Since symbol archives aren't really useful for Debug builds, add an
assert() against trying to create them in that configuration.

Bug: 936645, 772252
Change-Id: Ib18e3b512f8091fc24a9be2540b5748248cc060f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1512173
Reviewed-by: Kevin Marshall <kmarshall@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#639073}
5 files changed