[roll] Roll fuchsia [build][lto] Only support FatLTO for ELF targets with clang

Because we normally only enable LTO with the clang toolchain
when targeting ELF, it wasn't clear that other targets/toolchains
may sometimes receive FatLTO configs. This can happen when opting
targets out of FatLTO features, like the no-fat-lto-objects-linking
config. https://fxrev.dev/1121663 updates our test template to avoid
possible FatLTO linking when it is enabled, and thus exposed this
combination.

This patch opts GCC and non-ELF targets out of all FatLTO related
configs.

Original-Bug: 368146498, 364615885
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1121555
Original-Revision: 9eab015c586e821252405ddbf25762aef5d1bb40
GitOrigin-RevId: 5ec9a9c1288b86d130caad1c38024418abb253f1
Change-Id: I073b3faa9a3d7fd42417c2324496ca038bfd1313
diff --git a/stem b/stem
index 8b689c3..7fc5ccf 100644
--- a/stem
+++ b/stem
@@ -11,7 +11,7 @@
              githooks="integration/git-hooks"
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="d4cf79c167ea2007e872ddbb2c0a1f55730d185d"/>
+             revision="9eab015c586e821252405ddbf25762aef5d1bb40"/>
   </projects>
   <hooks>
     <hook name="install-environment"