[Tests][RuntimeDyld] Make sure we use a stub for cross-section branches.

We mustn't use direct branches for cross-section branches, because doing
so will result in problems if the sections aren't loaded at the same
offsets in the target process as in the host process.

rdar://127673408

Author: al45tair

llvm/test/ExecutionEngine/RuntimeDyld/AArch64/ELF_ARM64_xsec_branch.s

@@ -0,0 +1,20 @@
+# RUN: llvm-mc -triple=arm64-none-linux-gnu -filetype=obj -o %t %s
+# RUN: llvm-rtdyld -triple=arm64-none-linux-gnu -verify -check=%s %t
+
+.globl _main
+.weak _label1
+
+.section .text.label1,"ax"
+_label1:
+        nop
+
+.section .text.main,"ax"
+_main:
+        b _label1
+
+# Branch must be to stub in .text.main, *not* back to _label1, because
+# in general sections could be loaded at arbitrary addresses in target memory,
+# and when initially processing locations and generating stubs we don't know
+# the final layout yet, so we can't tell if the branch offset is within range.
+
+# rtdyld-check: *{4}(_main) = 0x14000001