Temporarily skip PGO on s390x

Resolves: RHEL-81600
Resolves: RHEL-81604

rust.spec

@@ -867,6 +867,9 @@ test -r "%{profiler}"
 
 %global __x %{__python3} ./x.py
 
+# Skipping PGO on s390x until we get LLVM 20, due to
+# https://github.com/llvm/llvm-project/issues/124001
+%ifnarch s390x
 %if %with rustc_pgo
 # Build the compiler with profile instrumentation
 %define profraw $PWD/build/profiles
@@ -882,6 +885,7 @@ rm -r "%{profraw}" build/%{rust_triple}/stage2*/
 # Redefine the macro to use that profile data from now on
 %global __x %{__x} --rust-profile-use="%{profdata}"
 %endif
+%endif
 
 # Build the compiler normally (with or without PGO)
 %{__x} build sysroot