Fix for non-constant SIGSTKSZ

On glibc > 2.33, `SIGSTKSZ` might not be constant (in which case
it expands to a call to `sysconf` which returns a `long int`); see
https://sourceware.org/pipermail/libc-alpha/2020-October/118513.html

Pass unsigned explicitly to std::max, to avoid relying on template
argument deduction. This works both with the old-style constant
`SIGSTKSZ` and the new configurable one.

Initially based on https://chromium-review.googlesource.com/c/2776379

Change-Id: I9fc95337f973e871b84735ce822b5e11ba73ea8c
Reviewed-on: https://chromium-review.googlesource.com/c/breakpad/breakpad/+/3340721
Reviewed-by: Mark Mentovai <mark@chromium.org>

src/client/linux/handler/exception_handler.cc

@@ -138,7 +138,7 @@ void InstallAlternateStackLocked() {
   // SIGSTKSZ may be too small to prevent the signal handlers from overrunning
   // the alternative stack. Ensure that the size of the alternative stack is
   // large enough.
-  static const unsigned kSigStackSize = std::max(16384, SIGSTKSZ);
+  const unsigned kSigStackSize = std::max<unsigned>(16384, SIGSTKSZ);
 
   // Only set an alternative stack if there isn't already one, or if the current
   // one is too small.