ANDROID: Add missing CFI jump table symbols to kallsyms

With CONFIG_LTO_CLANG_FULL, LLVM drops all CFI jump table symbols
from vmlinux, which doesn't affect kernel functionality, but can
make stack traces and other kernel output that prints out jump
table addresses harder to read.

This change works around the issue for now by adding a script that
tells kallsyms about the missing jump table symbols, even though
they don't actually exist in the symbol table, and generates a
linker script to add the missing symbols to kernel modules.

Bug: 186152035
Bug: 187415564
Change-Id: Ic3c51751c756f2f5fb2a31229e16c3397eb6e666
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>

scripts/module.lds.S

@@ -60,7 +60,10 @@ SECTIONS {
 	 */
 	.text : ALIGN(PAGE_SIZE) {
 		*(.text.__cfi_check)
-		*(.text .text.[0-9a-zA-Z_]* .text..L.cfi*)
+		*(.text .text.[0-9a-zA-Z_]*)
+		__cfi_jt_start = .;
+		*(.text..L.cfi.jumptable .text..L.cfi.jumptable.*)
+		__cfi_jt_end = .;
 	}
 #endif
 }