Revert "[NFC] remove explicit default value for strboolattr attribute in tests"

This reverts commit bda6e5bee04c75b1f1332b4fd1ac4e8ef6c3c247.

See https://lab.llvm.org/buildbot/#/builders/109/builds/15424 for instance
diff --git a/llvm/test/DebugInfo/X86/dwarf-linkage-names.ll b/llvm/test/DebugInfo/X86/dwarf-linkage-names.ll
index 0fae250..2af2b86 100644
--- a/llvm/test/DebugInfo/X86/dwarf-linkage-names.ll
+++ b/llvm/test/DebugInfo/X86/dwarf-linkage-names.ll
@@ -49,7 +49,7 @@
   ret i32 %0, !dbg !15
 }
 
-attributes #0 = { nounwind uwtable "disable-tail-calls"="false" "frame-pointer"="all" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+sse,+sse2" "use-soft-float"="false" }
+attributes #0 = { nounwind uwtable "disable-tail-calls"="false" "less-precise-fpmad"="false" "frame-pointer"="all" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+sse,+sse2" "unsafe-fp-math"="false" "use-soft-float"="false" }
 
 !llvm.dbg.cu = !{!5}
 !llvm.module.flags = !{!8, !9}