libfdt: Fix redefined uintptr_t warning for USE_HOSTCC

Compiling U-Boot in an old OS environment (RedHat-7.3  :-)  gives the
following warnings from FDT:

include/libfdt_env.h:50: warning: redefinition of 'uintptr_t'
/usr/include/stdint.h:129: warning: 'uintptr_t' previously declared here

Fix: Protect the definition of uintptr_t when compiling on the host
system.

Signed-off-by: Gerald Van Baren <vanbaren@cideas.com>

include/libfdt_env.h

@@ -47,6 +47,7 @@ extern struct fdt_header *working_fdt;  /* Pointer to the working fdt */
 #define cpu_to_fdt64(x)		(x)
 #endif
 
+#ifndef USE_HOSTCC
 /*
  * Types for `void *' pointers.
  *
@@ -58,5 +59,6 @@ typedef unsigned long int       uintptr_t;
 #else
 typedef unsigned int            uintptr_t;
 #endif
+#endif /* not USE_HOSTCC */
 
 #endif /* _LIBFDT_ENV_H */