compile gcc.target/arm/{pr78255-2.c,memset-inline-2.c} with -mno-long-calls

compile gcc.target/arm/{pr78255-2.c,memset-inline-2.c} with -mno-long-calls

If the target is configured such that -mlong-call is passed
by default, the function calls these tests are trying to detect
by scanning the assembly file are performed using long calls,
like so:

    | foo:
    |     @ memset-inline-2.c:12:   memset (a, -1, 14);
    |         mov     r2, #14 @,
    |         mvn     r1, #0  @,
    |         ldr     r0, .L2 @,
    |         ldr     r3, .L2+4       @ tmp112,
    |         bx      r3              @ tmp112

Looking at .L2 (and in particular at .L2+4):

    | .L2:
    |         .word   a
    |         .word   memset   <<<---

This change adds -mno-long-calls to the list of compiler options
to make sure we generate short call code, allowing the assembly
matching to pass.

This is added unconditionally to the dg-options (as opposed to using
dg-additional-options) because this test is already specific to ARM
targets, and -mno-long-calls is available on all ARM targets.

for  gcc/testsuite/ChangeLog

	* gcc.target/arm/memset-inline-2.c: Add -mno-long-calls to
	the test's dg-options.
	* gcc.target/arm/pr78255-2.c: Likewise.