glcpp: Clean up intermediate file when test suite is interrupted.

The glcpp-test script was leaving around bogus *.valgrind-errors files if
a valgrind test was interrupted.

src/glsl/glcpp/tests/glcpp-test

@@ -1,5 +1,7 @@
 #!/bin/sh
 
+trap 'rm $test.valgrind-errors; exit 1' INT QUIT
+
 total=0
 pass=0
 clean=0