valgrind: Make local functions static to avoid assembler error

valgrind: Make local functions static to avoid assembler error

Avoid mips32 x-compiler warnings such as:

| ../../../valgrind-3.14.0/helgrind/tests/annotate_hbefore.c:360:6: warning: no previous prototype for 'do_signal' [-Wmissing-prototypes]
|  void do_signal ( UWord* w )
|       ^~~~~~~~~

by making functions and global variables that are file scope be static
and more importantly also avoid an assembler error:

/tmp/cce22iiw.s: Assembler messages:
/tmp/cce22iiw.s:446: Error: symbol `exit_0' is already defined
/tmp/cce22iiw.s:448: Error: symbol `exit' is already defined
/tmp/cce22iiw.s:915: Error: symbol `exit_0' is already defined
/tmp/cce22iiw.s:917: Error: symbol `exit' is already defined

(From OE-Core rev: 5fface331c46b809c10b4f3d65904534d6933896)

Signed-off-by: Randy MacLeod <Randy.MacLeod@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>