Fix ASan alloca_constant_size.cc test on FreeBSD.
Fix ASan alloca_constant_size.cc test on FreeBSD.

On FreeBSD <alloca.h> does not exist: alloca(3) is defined in <stdlib.h>
instead.


git-svn-id: c199f293c43da69278bea8e88f92242bf3aa95f7@277300 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt