Force the Unicode version of GetEnvVar

src/win32/posix.c

diff --git a/src/win32/posix.c b/src/win32/posix.c
index 1c9430d..85a04bc 100644
--- a/src/win32/posix.c
+++ b/src/win32/posix.c
@@ -385,7 +385,7 @@
 
 	len++;  /* Null Terminator */
 	buf = malloc(sizeof(wchar_t) * len);
-	GetEnvironmentVariable(name_w, buf, len);
+	GetEnvironmentVariableW(name_w, buf, len);
 
 	ret = conv_utf16_to_utf8(buf);