[yaml2obj] Add support for sh_link via Link key.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184022 91177308-0d34-0410-b5e6-96231b3b80d8

test/Object/yaml2obj-elf-section-basic.yaml

@@ -10,6 +10,7 @@ Sections:
     Type: SHT_PROGBITS
     Flags: [ SHF_ALLOC, SHF_EXECINSTR ]
     Address: 0xCAFEBABE
+    Link: .text # Doesn't make sense for SHT_PROGBITS, but good enough for test.
     Content: EBFE
     AddressAlign: 2
 
@@ -26,6 +27,8 @@ Sections:
 # CHECK-NEXT:     ]
 # CHECK-NEXT:     Address: 0xCAFEBABE
 # CHECK:          Size: 2
+# Check that Link != 0.
+# CHECK:          Link: {{[1-9][0-9]*}}
 # CHECK:          AddressAlignment: 2
 # CHECK:          SectionData (
 # CHECK-NEXT:       0000: EBFE