[Obvious] arm: Fix test from failing on some targets [PR91816]

[Obvious] arm: Fix test from failing on some targets [PR91816]

This recently submitted test was found to fail on some Cortex-M
targets. This was because codegen on these CPUs would emit a ldr
instead of a movw/movt pair, resulting in an overall smaller test
(i.e. the branch wasn't as far) and the behaviour being tested
for not being triggered.

This commit doubles the size of the test to account for this.

gcc/testsuite/ChangeLog:

	* gcc.target/arm/pr91816.c: New test.