Author: Daniel Richard G. <skunk@iSKUNK.ORG>

When building Chromium on unstable/ppc64el with ThinLTO enabled, this error
occurs in the final link:

  ld.lld-16: error: Linking two modules of different data layouts:
  $C_CXX_OBJECT is 'e-m:e-i64:64-n32:64-S128-v256:256:256-v512:512:512' whereas
  $RUST_LIBRARY is 'e-m:e-Fn32-i64:64-n32:64-S128-v256:256:256-v512:512:512'

This is because the LLVM data layout for powerpc64le-unknown-linux-gnu has
evolved over time, gaining the "Fn32" bit that specifies function pointer
alignment. See the following source locations:

  llvm-project/clang/lib/Basic/Targets/PPC.h
  (class PPC64TargetInfo, under "Triple.getArch() == llvm::Triple::ppc64le")

  rust/compiler/rustc_target/src/spec/powerpc64le_unknown_linux_gnu.rs
  (note that this file was relocated in a later version)

This change occurred in clang-17, and rustc followed suit in 1.73.0. Since
we use an older clang and a newer rustc in our unstable build, we get an
inconsistency in data layouts when targeting this particular platform.

The error reported by the linker is not technically an error, however, only
a warning goosed up by a --fatal-warnings flag.

Index: chromium-128.0.6613.113/build/config/compiler/BUILD.gn
===================================================================
--- chromium-128.0.6613.113.orig/build/config/compiler/BUILD.gn
+++ chromium-128.0.6613.113/build/config/compiler/BUILD.gn
@@ -380,7 +380,7 @@ config("compiler") {
 
     # Linker warnings.
     if (fatal_linker_warnings && !is_apple && current_os != "aix" &&
-        current_os != "zos") {
+        current_os != "zos" && current_cpu != "ppc64") {
       ldflags += [ "-Wl,--fatal-warnings" ]
     }
     if (fatal_linker_warnings && is_apple) {