Add compatibility for systems lacking setenv() and unsetenv()

We'll want this for Windows/MinGW support.
Based on a patch from Nikos Mavrogiannopoulos.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

compat.c

@@ -24,6 +24,7 @@
 
 #include <string.h>
 #include <stdarg.h>
+#include <stdlib.h>
 #include <errno.h>
 #include <ctype.h>
 
@@ -168,3 +169,24 @@ char *openconnect__strcasestr(const char *haystack, const char *needle)
 	return NULL;
 }
 #endif
+
+#ifndef HAVE_SETENV
+int openconnect__setenv(const char *name, const char *value, int overwrite)
+{
+	char *buf = alloca(strlen(name) + strlen(value) + 2);
+
+	sprintf(buf, "%s=%s", name, value);
+	putenv(buf);
+	return 0;
+}
+#endif
+
+#ifndef HAVE_UNSETENV
+void openconnect__unsetenv(const char *name)
+{
+	char *buf = alloca(strlen(name) + 2);
+
+	sprintf(buf, "%s=", name);
+	putenv(buf);
+}
+#endif

configure.ac

@@ -144,6 +144,8 @@ AC_CHECK_FUNC(socket, [], AC_CHECK_LIB(socket, socket, [], AC_ERROR(Cannot find
 AC_CHECK_FUNC(inet_aton, [], AC_CHECK_LIB(nsl, inet_aton, [], AC_ERROR(Cannot find inet_aton() function)))
 AC_CHECK_FUNC(__android_log_vprint, [], AC_CHECK_LIB(log, __android_log_vprint, [], []))
 
+AC_CHECK_FUNCS(setenv unsetenv)
+
 AC_ENABLE_SHARED
 AC_DISABLE_STATIC
 

openconnect-internal.h

@@ -346,6 +346,14 @@ ssize_t openconnect__getline(char **lineptr, size_t *n, FILE *stream);
 #define strcasestr openconnect__strcasestr
 char *openconnect__strcasestr(const char *haystack, const char *needle);
 #endif
+#ifndef HAVE_SETENV
+#define setenv openconnect__setenv
+int openconnect__setenv(const char *name, const char *value, int overwrite);
+#endif
+#ifndef HAVE_UNSETENV
+#define unsetenv openconnect__unsetenv
+void openconnect__unsetenv(const char *name);
+#endif
 
 /* I always coded as if it worked like this. Now it does. */
 #define realloc_inplace(p, size) do {			\