Add CONFIG_NO_WORKER Makefile option

This option eliminates the dependency on the pthread library. This mode is
already toggled on _WIN32 and/or EMSCRIPTEN is detected, here we just allow the
user to toggle it at will at the top level.

This slightly reduce the code size as well, and may allow compiling this
library in some embedded contexts where pthread is not available or is broken.

Makefile

@@ -148,6 +148,9 @@ ifeq ($(shell $(CC) -o /dev/null compat/test-closefrom.c 2>/dev/null && echo 1),
 DEFINES+=-DHAVE_CLOSEFROM
 endif
 endif
+ifdef CONFIG_NO_WORKER
+DEFINES+=-DCONFIG_NO_WORKER
+endif
 
 CFLAGS+=$(DEFINES)
 CFLAGS_DEBUG=$(CFLAGS) -O0

quickjs-libc.c

@@ -64,7 +64,7 @@ typedef sig_t sighandler_t;
 
 #endif
 
-#if !defined(_WIN32)
+#if !defined(_WIN32) && !defined(CONFIG_NO_WORKER)
 /* enable the os.Worker API. IT relies on POSIX threads */
 #define USE_WORKER
 #endif

quickjs.c

@@ -68,7 +68,7 @@
 
 /* define to include Atomics.* operations which depend on the OS
    threads */
-#if !defined(EMSCRIPTEN)
+#if !defined(EMSCRIPTEN) && !defined(CONFIG_NO_WORKER)
 #define CONFIG_ATOMICS
 #endif