Disable compilation of static libraries with autotools.

configure.ac

@@ -4,6 +4,7 @@
 AC_PREREQ(2.59)
 AC_INIT(libmodbus, 1.9, stephane.raimbault@gmail.com)
 AM_INIT_AUTOMAKE(libmodbus, 1.9.0)
+AM_DISABLE_STATIC
 
 # Checks for programs.
 AC_PROG_CC