Fix tmpfile_other.cc

Error: explicitly-defaulted constructor cannot have default arguments

This broke chromium, and needs fixing before we can restart the autorollers.

Change-Id: I4b04dd127b5fb7cf84e5782e07bcf68b2befc904
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/48041
Auto-Submit: Ben Clayton <bclayton@google.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

src/utils/tmpfile_other.cc

@@ -17,7 +17,7 @@
 namespace tint {
 namespace utils {
 
-TmpFile::TmpFile(std::string) = default;
+TmpFile::TmpFile(std::string) {}
 
 TmpFile::~TmpFile() = default;