[cmake] Reenable FatLTO for Fuchsia toolchains

We can reenable this now that FatLTO won't be enabled for Mac platforms

Pull Request: #85709

Author: ilovepi

clang/cmake/caches/Fuchsia-stage2.cmake

@@ -11,7 +11,7 @@ set(LLVM_ENABLE_RUNTIMES "compiler-rt;libcxx;libcxxabi;libunwind" CACHE STRING "
 
 set(LLVM_ENABLE_BACKTRACES OFF CACHE BOOL "")
 set(LLVM_ENABLE_DIA_SDK OFF CACHE BOOL "")
-set(LLVM_ENABLE_FATLTO OFF CACHE BOOL "")
+set(LLVM_ENABLE_FATLTO ON CACHE BOOL "")
 set(LLVM_ENABLE_HTTPLIB ON CACHE BOOL "")
 set(LLVM_ENABLE_LIBCXX ON CACHE BOOL "")
 set(LLVM_ENABLE_LIBEDIT OFF CACHE BOOL "")