Avoid echoing stdin when output is piped to doas.

Fix asprintf() compile warning when building on Linux.

Makefile

@@ -3,12 +3,13 @@ YACC?=yacc
 BIN=doas
 PREFIX?=/usr/local
 OBJECTS=doas.o env.o execvpe.o reallocarray.o y.tab.o
-CFLAGS+=-DUSE_PAM -DDOAS_CONF=\"${PREFIX}/etc/doas.conf\"
+CFLAGS+=-DUSE_PAM -DDOAS_CONF=\"${PREFIX}/etc/doas.conf\" 
 LDFLAGS+=-lpam
 UNAME_S := $(shell uname -s)
 ifeq ($(UNAME_S),Linux)
     LDFLAGS+=-lpam_misc
     OBJECTS+=strlcat.o strlcpy.o
+    CFLAGS+=-D_GNU_SOURCE
 endif
 ifeq ($(UNAME_S),FreeBSD)
     CFLAGS+=-DHAVE_LOGIN_CAP_H

doas.c

@@ -433,7 +433,7 @@ main(int argc, char **argv)
 		pam_handle_t *pamh = NULL;
 		int pam_err;
 
-#ifndef linux
+/* #ifndef linux */
 		int temp_stdin;
 
 		/* openpam_ttyconv checks if stdin is a terminal and
@@ -450,7 +450,7 @@ main(int argc, char **argv)
 		if (temp_stdin == -1)
 			err(1, "dup");
 		close(STDIN_FILENO);
-#else
+/* #else */
 		/* force password prompt to display on stderr, not stdout */
 		int temp_stdout = dup(1);
 		if (temp_stdout == -1)
@@ -458,7 +458,7 @@ main(int argc, char **argv)
 		close(1);
 		if (dup2(2, 1) == -1)
 			err(1, "dup2");
-#endif
+/* #endif */
 
 		pam_err = pam_start("doas", myname, &pamc, &pamh);
 		if (pam_err != PAM_SUCCESS) {
@@ -510,17 +510,17 @@ main(int argc, char **argv)
 		}
 		pam_end(pamh, pam_err);
 
-#ifndef linux
+/* #ifndef linux */
 		/* Re-establish stdin */
 		if (dup2(temp_stdin, STDIN_FILENO) == -1)
 			err(1, "dup2");
 		close(temp_stdin);
-#else
+/* #else */
 		/* Re-establish stdout */
 		close(1);
 		if (dup2(temp_stdout, 1) == -1)
 			err(1, "dup2");
-#endif
+/* #endif */
 #else
 #error	No auth module!
 #endif

env.c

@@ -20,9 +20,9 @@
 #include <sys/tree.h>
 #endif
 
-#include <string.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <err.h>
 #include <unistd.h>
 #include <errno.h>
@@ -90,7 +90,7 @@ createenv(struct rule *rule)
 	env->count = 0;
 
 	if (rule->options & KEEPENV) {
-		extern const char **environ;
+		/* extern const char **environ; */
 
 		for (i = 0; environ[i] != NULL; i++) {
 			struct envnode *node;