Fix build on big endian systems

The usb_linux_client.c file defines cpu_to_le16/32 by using the C
library htole16/32 function calls. However, cpu_to_le16/32 are used
when initializing structures, i.e in a context where a function call
is not allowed.

It works fine on little endian systems because htole16/32 are defined
by the C library as no-ops. But on big-endian systems, they are
actually doing something, which might involve calling a function,
causing build failures.

To solve this, we simply open-code cpu_to_le16/32 in a way that allows
them to be used when initializing structures.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

Index: b/core/adb/usb_linux_client.c
===================================================================
--- a/core/adb/usb_linux_client.c
+++ b/core/adb/usb_linux_client.c
@@ -34,8 +34,15 @@
 #define MAX_PACKET_SIZE_FS	64
 #define MAX_PACKET_SIZE_HS	512
 
-#define cpu_to_le16(x)  htole16(x)
-#define cpu_to_le32(x)  htole32(x)
+#if __BYTE_ORDER == __LITTLE_ENDIAN
+# define cpu_to_le16(x) (x)
+# define cpu_to_le32(x) (x)
+#else
+# define cpu_to_le16(x) ((((x) >> 8) & 0xffu) | (((x) & 0xffu) << 8))
+# define cpu_to_le32(x) \
+	((((x) & 0xff000000u) >> 24) | (((x) & 0x00ff0000u) >>  8) | \
+	 (((x) & 0x0000ff00u) <<  8) | (((x) & 0x000000ffu) << 24))
+#endif
 
 struct usb_handle
 {