tests/http: fix out-of-tree builds

Add both lib/ directories (src & build) to the search path so
curl_setup.h and its dependencies can be found.

Followup-to acd82c8b

Ref: #11006
Closes #11036

tests/http/clients/Makefile.am

@@ -33,6 +33,8 @@ AUTOMAKE_OPTIONS = foreign nostdinc
 # $(top_srcdir)/include is for libcurl's external include files
 
 AM_CPPFLAGS = -I$(top_srcdir)/include   \
+              -I$(top_builddir)/lib     \
+              -I$(top_srcdir)/lib       \
               -DCURL_DISABLE_DEPRECATION
 
 LIBDIR = $(top_builddir)/lib

tests/http/clients/ws-data.c

@@ -36,7 +36,7 @@
 
 /* curl stuff */
 #include <curl/curl.h>
-#include "../../../lib/curl_setup.h"
+#include "curl_setup.h"
 
 #ifdef USE_WEBSOCKETS
 

tests/http/clients/ws-pingpong.c

@@ -36,7 +36,7 @@
 
 /* curl stuff */
 #include <curl/curl.h>
-#include "../../../lib/curl_setup.h"
+#include "curl_setup.h"
 
 #ifdef USE_WEBSOCKETS