pr103523: Check for PLUS/MINUS support

pr103523: Check for PLUS/MINUS support

Check for PLUS_EXPR/MINUS_EXPR support in vectorizable_induction.
PR103523 is an ICE on valid code:

void d(float *a, float b, int c) {
    float e;
    for (; c; c--, e += b)
      a[c] = e;
}

This is due to not checking for PLUS_EXPR support, which is missing in
VNx2sf mode. This causes an ICE at expand time. This patch adds a check
for support in vectorizable_induction.

gcc/ChangeLog:

	PR tree-optimization/103523
	* tree-vect-loop.c (vectorizable_induction): Check for
	PLUS_EXPR/MINUS_EXPR support.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/pr103523.c: New test.