wasm: increase default thread stack size to 1 MB

The default stack size for the main thread is 1 MB as specified by linker options.
However, the default stack size for threads was only 64 kB.

This is surprisingly small and thus we increase it to 1 MB to match the
main thread.

Author: surban

Diff for: std/src/sys/pal/wasi/thread.rs

@@ -67,7 +67,7 @@ cfg_if::cfg_if! {
     }
 }
 
-pub const DEFAULT_MIN_STACK_SIZE: usize = 64 * 1024;
+pub const DEFAULT_MIN_STACK_SIZE: usize = 1024 * 1024;
 
 impl Thread {
     // unsafe: see thread::Builder::spawn_unchecked for safety requirements

Diff for: std/src/sys/pal/wasm/atomics/thread.rs

@@ -6,7 +6,7 @@ use crate::time::Duration;
 
 pub struct Thread(!);
 
-pub const DEFAULT_MIN_STACK_SIZE: usize = 64 * 1024;
+pub const DEFAULT_MIN_STACK_SIZE: usize = 1024 * 1024;
 
 impl Thread {
     // unsafe: see thread::Builder::spawn_unchecked for safety requirements