[JITLink] Read symbol linkage from the correct field.

MachO symbol linkage is described by the desc field of the nlist entry, not the
type field.

Author: lhames

llvm/lib/ExecutionEngine/JITLink/MachOLinkGraphBuilder.cpp

@@ -274,7 +274,7 @@ Error MachOLinkGraphBuilder::createNormalizedSymbols() {
 
     IndexToSymbol[SymbolIndex] =
         &createNormalizedSymbol(*Name, Value, Type, Sect, Desc,
-                                getLinkage(Type), getScope(*Name, Type));
+                                getLinkage(Desc), getScope(*Name, Type));
   }
 
   return Error::success();

llvm/test/ExecutionEngine/JITLink/X86/Inputs/MachO_weak_defs_extra.s

@@ -0,0 +1,19 @@
+# Supplies a weak def, WeakDef, and a pointer holding its address,
+# WeakDefAddrInExtraFile.
+
+	.section	__TEXT,__text,regular,pure_instructions
+	.build_version macos, 10, 14	sdk_version 10, 14
+	.section	__DATA,__data
+	.globl	WeakDef
+	.weak_definition	WeakDef
+	.p2align	2
+WeakDef:
+	.long	2
+
+	.globl	WeakDefAddrInExtraFile
+	.p2align	3
+WeakDefAddrInExtraFile:
+	.quad	WeakDef
+
+
+.subsections_via_symbols

llvm/test/ExecutionEngine/JITLink/X86/MachO_weak_definitions.s

@@ -0,0 +1,39 @@
+# RUN: rm -rf %t && mkdir -p %t
+# RUN: llvm-mc -triple x86_64-apple-macosx10.9 -filetype=obj \
+# RUN:   -o %t/MachO_weak_defs_extra.o %S/Inputs/MachO_weak_defs_extra.s
+# RUN: llvm-mc -triple x86_64-apple-macosx10.9 -filetype=obj \
+# RUN:   -o %t/MachO_weak_definitions.o %s
+# RUN: llvm-jitlink -noexec -check=%s %t/MachO_weak_definitions.o \
+# RUN:   %t/MachO_weak_defs_extra.o
+#
+# Check that objects linked separately agree on the address of weak symbols.
+#
+# jitlink-check: *{8}WeakDefAddrInThisFile = *{8}WeakDefAddrInExtraFile
+
+	.section	__TEXT,__text,regular,pure_instructions
+	.build_version macos, 10, 14	sdk_version 10, 14
+	.globl	_main
+	.p2align	4, 0x90
+_main:
+	retq
+
+	.section	__DATA,__data
+	.globl	WeakDef
+	.weak_definition	WeakDef
+	.p2align	2
+WeakDef:
+	.long	1
+
+	.globl	WeakDefAddrInThisFile
+	.p2align	3
+WeakDefAddrInThisFile:
+	.quad	WeakDef
+
+# Take the address of WeakDefAddrInExtraFile to force its materialization
+	.globl	extra_file_anchor
+	.p2align	3
+extra_file_anchor:
+	.quad	WeakDefAddrInExtraFile
+
+
+.subsections_via_symbols