Handle errors from close in perlasm scripts.

If the xlate filter script fails, the outer script swallows the error,
unless we check the return value of close.

Change-Id: Ib506bb745a5d27b9d1df9329535bf81ad090f41f
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/35724
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/crypto/fipsmodule/sha/asm/sha1-x86_64.pl b/crypto/fipsmodule/sha/asm/sha1-x86_64.pl
index fd4ff2a..df7cbc3 100755
--- a/crypto/fipsmodule/sha/asm/sha1-x86_64.pl
+++ b/crypto/fipsmodule/sha/asm/sha1-x86_64.pl
@@ -2122,4 +2122,4 @@
 
 	print $_,"\n";
 }
-close STDOUT;
+close STDOUT or die "error closing STDOUT";