[JITLink][MachO] Add missing testcase.

This test was accidentally left out of f9649d123db.

test/ExecutionEngine/JITLink/X86/MachO_cstring_section_splitting.s

@@ -0,0 +1,44 @@
+# REQUIRES: asserts
+# RUN: llvm-mc -triple=x86_64-apple-macosx10.9 -filetype=obj -o %t %s
+# RUN: llvm-jitlink -debug-only=jitlink -noexec -entry hook %t 2>&1 | \
+# RUN:   FileCheck %s
+#
+# Verify that we split C string literals on null-terminators, rather than on
+# symbol boundaries. We expect four dead-stripped symbols: l_str.0, l_str.2,
+# L_str.3, l_str.4, and the auto-generated symbol for the start of the "defghi"
+# string. We also verify that there are only two dead-stripped blocks, since
+# l_str.3 should not have split the block started at "def"... (since this is a
+# C string section we should be splitting on null characters instead of
+# symbols).
+#
+# CHECK:      Dead-stripping defined symbols:
+# CHECK-NEXT: linkage: strong, scope: local, dead
+# CHECK-NEXT: linkage: strong, scope: local, dead
+# CHECK-NEXT: linkage: strong, scope: local, dead
+# CHECK-NEXT: linkage: strong, scope: local, dead
+# CHECK-NEXT: Dead-stripping blocks:
+# CHECK-NEXT: content, align = 1, align-ofs = 0, section = __TEXT,__cstring
+# CHECK-NEXT: content, align = 1, align-ofs = 0, section = __TEXT,__cstring
+# CHECK-NEXT: Removing unused external symbols
+
+        .section        __DATA,__data
+        .globl  hook
+        .p2align        2
+hook:
+        .quad   l_str.1
+
+        .section        __TEXT,__cstring,cstring_literals
+l_str.0:
+l_str.1:
+        .asciz  "abc"
+l_str.2:
+        .asciz  ""
+# anonymous start for "defghi", split in the middle by l_str.3. We expect this
+# to be dead-stripped as a single block.
+        .byte   'd'
+        .byte   'e'
+        .byte   'f'
+l_str.3:
+        .asciz  "ghi"
+
+.subsections_via_symbols