[sanitizer] fix asan on the platforms where the page size is not a compile-time constant (or at least where EXEC_PAGESIZE may not be trustworthy), e.g. powerpc64. 
[sanitizer] fix asan on the platforms where the page size is not a compile-time constant (or at least where EXEC_PAGESIZE may not be trustworthy), e.g. powerpc64. 

git-svn-id: c199f293c43da69278bea8e88f92242bf3aa95f7@182351 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