Reapply emscripten libc include changes

Author: kleisauke

system/lib/libc/musl/include/setjmp.h

@@ -20,7 +20,7 @@ typedef struct __jmp_buf_tag {
  || defined(_BSD_SOURCE)
 typedef jmp_buf sigjmp_buf;
 /* XXX EMSCRIPTEN: No signals support, alias sigsetjmp and siglongjmp to their non-signals counterparts. */
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 #define sigsetjmp(buf, x) setjmp((buf))
 #define siglongjmp(buf, val) longjmp(buf, val)
 #else

system/lib/libc/musl/include/unistd.h

@@ -236,20 +236,20 @@ pid_t gettid(void);
 #define _POSIX_NO_TRUNC         1
 #define _POSIX_RAW_SOCKETS      _POSIX_VERSION
 
-#ifndef __EMSCRIPTEN__
-#define _POSIX_REALTIME_SIGNALS _POSIX_VERSION
-#else
+#ifdef __EMSCRIPTEN__
 #define _POSIX_REALTIME_SIGNALS -1
+#else
+#define _POSIX_REALTIME_SIGNALS _POSIX_VERSION
 #endif
 
 #define _POSIX_REGEXP           1
 #define _POSIX_SAVED_IDS        1
 #define _POSIX_SHELL            1
 
-#ifndef __EMSCRIPTEN__
-#define _POSIX_SPAWN            _POSIX_VERSION
-#else
+#ifdef __EMSCRIPTEN__
 #define _POSIX_SPAWN            -1
+#else
+#define _POSIX_SPAWN            _POSIX_VERSION
 #endif
 
 #define _POSIX_VDISABLE         0