Fix expected output of massif/tests/mmapunmap on Solaris.

Fix expected output of massif/tests/mmapunmap on Solaris.

On Solaris and Linux, mmap() is an optimized function without
prologue and epilogue. However, Solaris libc does not currently
bear any DWARF CFI. Therefore stack chain unwinder grabs only
two entries: IP inside mmap() and return address from the previous
frame which points inside _start(), right after where main()
is invoked. By introducing an intermediate function f(), main()
is now visible in the stack trace even on Solaris.
n-i-bz

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@15749