[Sanitizer] Fix GetRSS on Linux with non-4k pages

[foad]

Summary

The numbers in /proc/self/statm are in pages, not in fixed 4k units.
This fixes Linux/hard_rss_limit_mb_test.cc on my PowerPC64 box which
has 64k pages.

[willschm]

This looks like a good change to me.
Thanks,
-Will

lib/sanitizer_common/sanitizer_linux.cc

uptr GetRSS() {
   char buf[64];
   uptr len = internal_read(fd, buf, sizeof(buf) - 1);
   internal_close(fd);
   if ((sptr)len <= 0)
     return 0;
   buf[len] = 0;
   // The format of the file is:
   // 1084 89 69 11 0 79 0
-  // We need the second number which is RSS in 4K units.
+  // We need the second number which is RSS in pages.
   char *pos = buf;
   // Skip the first number.
   while (*pos >= '0' && *pos <= '9')
     pos++;
   // Skip whitespaces.
   while (!(*pos >= '0' && *pos <= '9') && *pos != 0)
     pos++;
   // Read the number.
   uptr rss = 0;
   while (*pos >= '0' && *pos <= '9')
     rss = rss * 10 + *pos++ - '0';
-  return rss * 4096;
+  return rss * GetPageSizeCached();
 }
 
 static void GetArgsAndEnv(char*** argv, char*** envp) {
 #if !SANITIZER_GO
   if (&__libc_stack_end) {
 #endif
     uptr* stack_end = (uptr*)__libc_stack_end;
     int argc = *stack_end;