xmlrpc-c: Update to 1.51.03

Small Makefile reorganization.

Switch BUILD_PARALLEL to 1. Seems to work now.

Added nanosleep patch that replaces usleep usage.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

libs/xmlrpc-c/patches/010-nanosleep.patch

@@ -0,0 +1,20 @@
+--- a/lib/libutil/sleep.c
++++ b/lib/libutil/sleep.c
+@@ -8,7 +8,7 @@
+ #  include <windows.h>
+ #  include <process.h>
+ #else
+-#  include <unistd.h>
++#  include <time.h>
+ #endif
+ 
+ 
+@@ -18,6 +18,7 @@ xmlrpc_millisecond_sleep(unsigned int const milliseconds) {
+ #if MSVCRT
+     SleepEx(milliseconds, true);
+ #else
+-    usleep(milliseconds * 1000);
++    const struct timespec req = {0, milliseconds * 1000 * 1000};
++    nanosleep(&req, NULL);
+ #endif
+ }