[testsuite] Fix sibcall-9 & sibcall-10 with -fPIC

[testsuite] Fix sibcall-9 & sibcall-10 with -fPIC

gcc.dg/sibcall-9.c and gcc.dg/sibcall-10.c give execution failure
on ARM when compiled with -fPIC due to the PIC access to volatile
variable v creating an extra spill which causes the frame size of the
two recursive functions to be different. Making the variable static
solve the issue because the variable can be access in a PC-relative way
and avoid the spill, while still testing sibling call as originally
intended.

2018-10-25  Thomas Preud'homme  <thomas.preudhomme@linaro.org>

gcc/testsuite/
    * gcc.dg/sibcall-9.c: Make v static.
    * gcc.dg/sibcall-10.c: Likewise.

From-SVN: r265482