s390/entry: workaround llvm's IAS limitations

llvm's integrated assembler cannot handle immediate values which are
calculated with two local labels:

<instantiation>:3:13: error: invalid operand for instruction
 clgfi %r14,.Lsie_done - .Lsie_gmap

Workaround this by adding clang specific code which reads the specific
value from memory. Since this code is within the hot paths of the kernel
and adds an additional memory reference, keep the original code, and add
ifdef'ed code.

Acked-by: Alexander Gordeev <agordeev@linux.ibm.com>
Link: https://lore.kernel.org/r/20220511120532.2228616-5-hca@linux.ibm.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

Author: hcahca

arch/s390/kernel/entry.S

@@ -172,9 +172,19 @@ _LPP_OFFSET	= __LC_LPP
 	lgr	%r14,\reg
 	larl	%r13,\start
 	slgr	%r14,%r13
-	lghi	%r13,\end - \start
-	clgr	%r14,%r13
+#ifdef CONFIG_AS_IS_LLVM
+	clgfrl	%r14,.Lrange_size\@
+#else
+	clgfi	%r14,\end - \start
+#endif
 	jhe	\outside_label
+#ifdef CONFIG_AS_IS_LLVM
+	.section .rodata, "a"
+	.align 4
+.Lrange_size\@:
+	.long	\end - \start
+	.previous
+#endif
 	.endm
 
 	.macro SIEEXIT