[Polly][test] Add missing REQUIRES line (#210578)

The test was added by #201859. It's test uses --debug-only which
requires an LLVM_ENABLE_ASSERTIONS-build

(cherry picked from commit 5cae63bd0d31118a15481fc7e5b063a73492d77d)

polly/test/IstAstInfo/AstGenComputeOut.ll

@@ -21,6 +21,8 @@
 ; value that still arms the guard (0 means unbounded) -- so the quota trips
 ; as early as possible and the test does not depend on an arbitrary tuned cutoff value.
 
+; REQUIRES: asserts
+
 ; RUN: opt %loadNPMPolly %s -passes='polly-custom<ast>' -polly-process-unprofitable \
 ; RUN:   -polly-astgen-computeout=1 -debug-only=polly-ast \
 ; RUN:   -disable-output 2>&1 | FileCheck %s