Autoconf: Review all inline test code

The inlined test sources in m4/jtr_arm_logic.m4 and similar files (there's two or three more) should be reviewed.

Example:

#include <arm_neon.h>
#include <stdio.h>

extern void exit(int);

int main() {
    uint32x4_t t;
    *((long*)&t) = 1;
    t = veorq_u32(t, t);
    if ((*(unsigned*)&t) == 88)
        printf(".");
    exit(0);
}

This particular one tests if we have veorq_u32().

What it really does is look for build fail or good exit code (vs. segfault): The "88" is only there to ensure things aren't optimized away, it doesn't test correctness.

All such programs should be trivially rewritten so we:

• Get rid of aliasing violations.
• Do a test that actually tests the correctness (it's not very important but just because we can).
• Instead of the printf, exit with the calculated value (expected 0) or based on it (0 for good, 1 for bad).

Start with the inline test source in m4/jtr_arm_logic.m4, then locate the two or three similar files mentioned in the issue. Review each program for aliasing violations and whether it checks the intrinsic's result rather than only build success or a non-optimized execution. Done means every such test uses a correctness-based exit status and no longer relies on the described printf or invalid aliasing.