arm: testuite: Missing optimization pattern for rev16 with thumb1

arm: testuite: Missing optimization pattern for rev16 with thumb1

This patch marks a rev16 test as XFAIL for architectures having only
Thumb1 support.  The generated code is functionally correct, but the
optimization is disabled when -mthumb is equivalent to Thumb1.  Fixing
the root issue would requires changes that are not suitable for GCC14
stage 4.  More information at
https://linaro.atlassian.net/browse/GNU-1141

gcc/testsuite/ChangeLog:

	* gcc.target/arm/rev16_2.c: XFAIL when compiled with Thumb1.