Add WASI platform support.

This includes the following significant changes:
  * Patching ezsat and minisat to disable resource limiting code
    on WASM/WASI, since the POSIX functions they use are unavailable.
  * Adding a new definition, YOSYS_DISABLE_SPAWN, present if platform
    does not support spawning subprocesses (i.e. Emscripten or WASI).
    This definition hides the definition of `run_command()`.
  * Adding a new Makefile flag, DISABLE_SPAWN, present in the same
    condition. This flag disables all passes that require spawning
    subprocesses for their function.

1 files changed, 34 insertions, 0 deletions

diff --git a/libs/minisat/00_PATCH_wasm.patch b/libs/minisat/00_PATCH_wasm.patch
new file mode 100644
index 000000000..0bcff7d77
--- /dev/null
+++ b/libs/minisat/00_PATCH_wasm.patch
@@ -0,0 +1,34 @@
+--- System.cc
++++ System.cc
+@@ -101,7 +101,7 @@ double Minisat::memUsedPeak(bool) { return 0; }
+ #endif
+
+
+-#if !defined(_MSC_VER) && !defined(__MINGW32__)
++#if !defined(_MSC_VER) && !defined(__MINGW32__) && !defined(__wasm)
+ void Minisat::limitMemory(uint64_t max_mem_mb)
+ {
+ // FIXME: OpenBSD does not support RLIMIT_AS. Not sure how well RLIMIT_DATA works instead.
+@@ -133,7 +133,7 @@ void Minisat::limitMemory(uint64_t /*max_mem_mb*/)
+ #endif
+
+
+-#if !defined(_MSC_VER) && !defined(__MINGW32__)
++#if !defined(_MSC_VER) && !defined(__MINGW32__) && !defined(__wasm)
+ void Minisat::limitTime(uint32_t max_cpu_time)
+ {
+     if (max_cpu_time != 0){
+@@ -156,9 +156,13 @@ void Minisat::limitTime(uint32_t /*max_cpu_time*/)
+
+ void Minisat::sigTerm(void handler(int))
+ {
++#if defined(__wasm)
++    (void)handler;
++#else
+     signal(SIGINT, handler);
+     signal(SIGTERM,handler);
+ #ifdef SIGXCPU
+     signal(SIGXCPU,handler);
+ #endif
++#endif
+ }