Turn on gc-sections support.

The two commits in this branch turn on support for gc-sections which has been turned off since commit 52ff10458ff6eb1866e510b831dbf4633cbd524b.

The first commit adds an ARC linker test for an issue that was causing an assertion to fire when --gc-sections was used in some cases, after the first commit the test is added, but will fail.

The second commit fixes the issue that is causing the assertion to fire (see 7360d724815ea7b092a39a7871d3c119f4ae6936 for details) and then turns on support for gc-sections.