build: don't build libhostname unless shared libcurl is built

configure.ac

@@ -2461,6 +2461,13 @@ AM_CONDITIONAL(USE_MANUAL, test x"$USE_MANUAL" = x1)
 CURL_CHECK_LIB_ARES
 AM_CONDITIONAL(USE_EMBEDDED_ARES, test x$embedded_ares = xyes)
 
+if test "x$enable_shared" = "xyes"; then
+  build_libhostname=yes
+else
+  build_libhostname=no
+fi
+AM_CONDITIONAL(BUILD_LIBHOSTNAME, test x$tests_use_libhostname = xyes)
+
 CURL_CHECK_OPTION_THREADED_RESOLVER
 
 if test "x$want_thres" = xyes && test "x$want_ares" = xyes; then

tests/libtest/Makefile.am

@@ -64,7 +64,11 @@ include Makefile.inc
 # Preloading of libhostname allows host name overriding,
 # this is used to make some tests machine independent.
 
+if BUILD_LIBHOSTNAME
 noinst_LTLIBRARIES = libhostname.la
+else
+noinst_LTLIBRARIES =
+endif
 
 if NO_UNDEFINED
 # The -no-undefined flag is crucial to build fine on some platforms