Drop LLVM_RAM_PER_COMPILE_JOB option on s390x

The underlying NUMBER_OF_LOGICAL_CORES query in cmake does not work on
s390x, which causes the build pool to be limited to 1 job.  This was
causing extremely slow builds on s390x/RHEL8.

Author: tstellar

llvm.spec

@@ -1344,8 +1344,13 @@ popd
 %endif
 
 %if 0%{?rhel} == 8
+%ifnarch s390x
+	# This option uses the NUMBER_OF_LOGICAL_CORES query in CMake which doesn't
+	# work on s390x.
+	# https://gitlab.kitware.com/cmake/cmake/-/issues/26619
 	%global cmake_config_args %{cmake_config_args} -DLLVM_RAM_PER_COMPILE_JOB=2048
 %endif
+%endif
 #endregion misc options
 
 extra_cmake_args=''