Test for _WIN32 in instead of USE_MINGW.

Bug: http://b/23392815
Test: builds
Change-Id: I7fce8de1f0e2314170cce456cd49346dcee9d134
diff --git a/libsparse/output_file.c b/libsparse/output_file.c
index d284736..6578d99 100644
--- a/libsparse/output_file.c
+++ b/libsparse/output_file.c
@@ -34,7 +34,7 @@
 #include "sparse_crc32.h"
 #include "sparse_format.h"
 
-#ifndef USE_MINGW
+#ifndef _WIN32
 #include <sys/mman.h>
 #define O_BINARY 0
 #else
@@ -705,7 +705,7 @@
 	aligned_diff = offset - aligned_offset;
 	buffer_size = len + aligned_diff;
 
-#ifndef USE_MINGW
+#ifndef _WIN32
 	char *data = mmap64(NULL, buffer_size, PROT_READ, MAP_SHARED, fd,
 			aligned_offset);
 	if (data == MAP_FAILED) {
@@ -733,7 +733,7 @@
 
 	ret = out->sparse_ops->write_data_chunk(out, len, ptr);
 
-#ifndef USE_MINGW
+#ifndef _WIN32
 	munmap(data, buffer_size);
 #else
 	free(data);