[llvm-objcopy] [COFF] Test absolute symbols wrt --strip-unneeded and --discard-all. NFC.

[mstorsjo]

Summary

These seem to be handled correctly vs GNU objcopy as the code stands right now.

[jhenderson]

LGTM. I'm assuming that the -1 SectionNumber is what makes them absolute?

[mstorsjo]

In D56659#1356023, @jhenderson wrote:

LGTM. I'm assuming that the -1 SectionNumber is what makes them absolute?

Exactly - section indices are positive for actual defined sections, zero for undefined and negative for a few special cases. (-1 for absolute and -2 for a debug kind of symbol.)

llvm/trunk/test/tools/llvm-objcopy/COFF/Inputs/discard-locals.yaml

- Name:            local_referenced
     ComplexType:     IMAGE_SYM_DTYPE_NULL
     StorageClass:    IMAGE_SYM_CLASS_STATIC
   - Name:            local_undefined_unreferenced
     Value:           0
     SectionNumber:   0
     SimpleType:      IMAGE_SYM_TYPE_NULL
     ComplexType:     IMAGE_SYM_DTYPE_NULL
     StorageClass:    IMAGE_SYM_CLASS_STATIC
+  - Name:            '@feat.00'
+    Value:           0
+    SectionNumber:   -1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
 ...

llvm/trunk/test/tools/llvm-objcopy/COFF/discard-all.test

 RUN: cmp %t.out.o %t.strip-discard-all.o
 
 SYMBOLS: SYMBOL TABLE:
 SYMBOLS-NEXT: external
 SYMBOLS-NEXT: external_undefined
 SYMBOLS-PRE-NEXT: local_unreferenced
 SYMBOLS-NEXT: local_referenced
 SYMBOLS-NEXT: local_undefined_unreferenced
+SYMBOLS-PRE-NEXT: @feat.00
 SYMBOLS-EMPTY:

llvm/trunk/test/tools/llvm-objcopy/COFF/strip-unneeded.test

 RUN: yaml2obj %p/Inputs/discard-locals.yaml > %t.in.o
 
 RUN: llvm-objdump -t %t.in.o | FileCheck %s --check-prefixes=SYMBOLS,SYMBOLS-PRE
 
 RUN: llvm-objcopy --strip-unneeded %t.in.o %t.out.o
 RUN: llvm-objdump -t %t.out.o | FileCheck %s --check-prefix=SYMBOLS
 
 SYMBOLS: SYMBOL TABLE:
 SYMBOLS-NEXT: external
 SYMBOLS-NEXT: external_undefined
 SYMBOLS-PRE-NEXT: local_unreferenced
 SYMBOLS-NEXT: local_referenced
 SYMBOLS-PRE-NEXT: local_undefined_unreferenced
+SYMBOLS-PRE-NEXT: @feat.00
 SYMBOLS-EMPTY: