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/Bitcode/drop-debug-info.3.5.ll b/llvm/test/Bitcode/drop-debug-info.3.5.ll
index 9794b0f..35d3958 100644
--- a/llvm/test/Bitcode/drop-debug-info.3.5.ll
+++ b/llvm/test/Bitcode/drop-debug-info.3.5.ll
@@ -19,7 +19,7 @@
   ret i32 0, !dbg !12
 }
 
-attributes #0 = { nounwind ssp uwtable "frame-pointer"="all" "stack-protector-buffer-size"="8" "use-soft-float"="false" }
+attributes #0 = { nounwind ssp uwtable "less-precise-fpmad"="false" "frame-pointer"="all" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
 
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!9, !10}