Add _AST_nofastspawn, which is used if the only method is fork(2)

src/lib/libast/comp/spawnveg.c

@@ -98,9 +98,7 @@ spawnveg_fast(const char* path, char* const argv[], char* const envv[], pid_t pg
 	return -1;
 }
 
-#else
-
-#if _lib_spawn_mode
+#elif _lib_spawn_mode
 
 #include <process.h>
 
@@ -112,7 +110,7 @@ spawnveg_fast(const char* path, char* const argv[], char* const envv[], pid_t pg
 #endif
 
 static pid_t
-spawnveg_fast (const char* path, char* const argv[], char* const envv[], pid_t pgid, int tcfd)
+spawnveg_fast(const char* path, char* const argv[], char* const envv[], pid_t pgid, int tcfd)
 {
 	NOT_USED(tcfd);
 #if defined(P_DETACH)
@@ -123,9 +121,7 @@ spawnveg_fast (const char* path, char* const argv[], char* const envv[], pid_t p
 #endif
 }
 
-#else
-
-#if _lib_spawn && _hdr_spawn && _mem_pgroup_inheritance
+#elif _lib_spawn && _hdr_spawn && _mem_pgroup_inheritance
 
 #include <spawn.h>
 
@@ -148,13 +144,14 @@ spawnveg_fast(const char* path, char* const argv[], char* const envv[], pid_t pg
 	return spawn(path, 0, NULL, &inherit, (const char**)argv, (const char**)envv);
 }
 
-#endif
+#else
 
-#endif
+#undef _AST_nofastspawn
+#define _AST_nofastspawn 1
 
 #endif
 
-#if !(_lib_posix_spawn_file_actions_addtcsetpgrp_np && defined(POSIX_SPAWN_SETSID))
+#if !(_lib_posix_spawn_file_actions_addtcsetpgrp_np && defined(POSIX_SPAWN_SETSID)) || defined(_AST_nofastspawn)
 
 #include <error.h>
 #include <wait.h>
@@ -270,6 +267,9 @@ spawnveg_slow(const char* path, char* const argv[], char* const envv[], pid_t pg
 pid_t
 spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid, int tcfd)
 {
+#ifdef _AST_nofastspawn
+	return spawnveg_slow(path, argv, envv, pgid, tcfd);
+#else
 #if !_lib_posix_spawn_file_actions_addtcsetpgrp_np
 	if(tcfd > -1)
 		/*
@@ -287,4 +287,5 @@ spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid, i
 		return spawnveg_slow(path, argv, envv, pgid, tcfd);
 #endif
 	return spawnveg_fast(path, argv, envv, pgid, tcfd);
+#endif /* _AST_nofastspawn */
 }