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.

libs/ezsat/ezminisat.cc

@@ -29,11 +29,12 @@
 
 #include <limits.h>
 #include <stdint.h>
-#include <csignal>
 #include <cinttypes>
 
-#ifndef _WIN32
+#if !defined(_WIN32) && !defined(__wasm)
+#  include <csignal>
 #  include <unistd.h>
+#  define HAS_ALARM
 #endif
 
 #include "../minisat/Solver.h"
@@ -84,7 +85,7 @@ bool ezMiniSAT::eliminated(int idx)
 }
 #endif
 
-#ifndef _WIN32
+#if defined(HAS_ALARM)
 ezMiniSAT *ezMiniSAT::alarmHandlerThis = NULL;
 clock_t ezMiniSAT::alarmHandlerTimeout = 0;
 
@@ -183,7 +184,7 @@ contradiction:
 #endif
 	}
 
-#ifndef _WIN32
+#if defined(HAS_ALARM)
 	struct sigaction sig_action;
 	struct sigaction old_sig_action;
 	int old_alarm_timeout = 0;
@@ -202,7 +203,7 @@ contradiction:
 
 	bool foundSolution = minisatSolver->solve(assumps);
 
-#ifndef _WIN32
+#if defined(HAS_ALARM)
 	if (solverTimeout > 0) {
 		if (alarmHandlerTimeout == 0)
 			solverTimoutStatus = true;

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
+ }

libs/minisat/00_UPDATE.sh

@@ -16,4 +16,4 @@ patch -p0 < 00_PATCH_mkLit_default_arg.patch
 patch -p0 < 00_PATCH_remove_zlib.patch
 patch -p0 < 00_PATCH_no_fpu_control.patch
 patch -p0 < 00_PATCH_typofixes.patch
-
+patch -p0 < 00_PATCH_wasm.patch

libs/minisat/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
 }