[llvm-objcopy] Don't remove .gnu_debuglink section when using --strip-all (#78919)

This fixes the issue mentioned here:
#57407
It prevents `llvm-objcopy` from removing the `.gnu _debuglink` section
when used with the `--strip-all` flag. Since `--strip-all` is the
default of `llvm-strip` the patch also prevents `llvm-strip` from
removing the `.gnu_debuglink` section.

Author: Felix Kellenbenz

llvm/lib/ObjCopy/ELF/ELFObjcopy.cpp

@@ -450,6 +450,8 @@ static Error replaceAndRemoveSections(const CommonConfig &Config,
         return false;
       if (StringRef(Sec.Name).starts_with(".gnu.warning"))
         return false;
+      if (StringRef(Sec.Name).starts_with(".gnu_debuglink"))
+        return false;
       // We keep the .ARM.attribute section to maintain compatibility
       // with Debian derived distributions. This is a bug in their
       // patchset as documented here:

llvm/test/tools/llvm-objcopy/ELF/strip-all.test

@@ -68,16 +68,19 @@ Sections:
     Flags:           [ ]
   - Name:            .gnu.warning.foo
     Type:            SHT_PROGBITS
+  - Name:            .gnu_debuglink
+    Type:            SHT_PROGBITS
 ProgramHeaders:
   # Use an arbitrary segment type to show that the segment type is unimportant.
   - Type:     0x61234567
     FirstSec: non_alloc_in_segment
     LastSec:  non_alloc_in_segment
 
-# CHECK: SectionHeaderCount: 6
+# CHECK: SectionHeaderCount: 7
 
 # CHECK: Name: non_alloc_in_segment
 # CHECK: Name: .bss
 # CHECK: Name: .text
 # CHECK: Name: .gnu.warning.foo
+# CHECK: Name: .gnu_debuglink
 # CHECK: Name: .shstrtab