Fuzzing tests generate shaders with large arrays or very high numbers of
local variables, which can cause stack overflow. We need to limit the
allowable stack memory usage of generated routines.

Note this change does not yet gracefully deal with routines which exceed
this limit. They will cause a null pointer dereference instead of a
stack overflow.

The default stack size limit of 1 MiB at the Subzero level is to ensure
we catch cases of excessive stack sizes even in the case no explicit
limit was set. At the Reactor level we reduce it to 512 KiB to prevent
actual stack overflow for a 1 MiB stack, assuming some earlier calls
might want to use the stack. Also, our legacy 'ASM' compiler for GLSL
allocates 4096 'registers' of 4 components for 128-bit SIMD, which
already requires 256 KiB.

Bug: b/157555596
Change-Id: I474285eecc786496edffbaef29719ca0cdf03f7d
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/52329
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Commit-Queue: Nicolas Capens <nicolascapens@google.com>