[Sanitizers] Fix sanitizer_posix_libcdep.cc compilation on Solaris 11.5

A recent build of Solaris 11.5 Beta (st_047) gained madvise(MADV_DONTDUMP)
support for Linux compatibility.  This broke the compiler-rt build:

  /vol/llvm/src/llvm/dist/projects/compiler-rt/lib/sanitizer_comm/sanitizer_posix_libcdep.cc: In function ‘bool __sanitizer::DontDumpShadowMemory(__sanitizer::uptr, __sanitizer::uptr)’:
  /vol/llvm/src/llvm/dist/projects/compiler-rt/lib/sanitizer_common/sanitizer_posix_libcdep.cc:81:18: error: invalid conversion from ‘void*’ to ‘caddr_t’ {aka ‘char*’} [-fpermissive]
     81 |   return madvise((void *)addr, length, MADV_DONTDUMP) == 0;
        |                  ^~~~~~~~~~~~
        |                  |
        |                  void*
  In file included from
/vol/llvm/src/llvm/dist/projects/compiler-rt/lib/sanitizer_common/sanitizer_posix_libcdep.cc:32:
  /usr/include/sys/mman.h:231:20: note: initializing argument 1 of ‘int
madvise(caddr_t, std::size_t, int)’
    231 | extern int madvise(caddr_t, size_t, int);
        |                    ^~~~~~~

The obvious fix is to use the same solution that has already been used a
couple of lines earlier:

  // In the default Solaris compilation environment, madvise() is declared
  // to take a caddr_t arg; casting it to void * results in an invalid
  // conversion error, so use char * instead.

This allowed the compiler-rt build to finish and was tested successfully on 
i386-pc-solaris2.11 and x86_64-pc-linux-gnu.

Differential Revision: https://reviews.llvm.org/D62892

llvm-svn: 363778