Check lib64 dir for libplatform as well.

config.m4

@@ -145,8 +145,12 @@ AC_LINK_IFELSE([AC_LANG_PROGRAM([[#include <v8-debug.h>]],
       AC_MSG_CHECKING([for $static_link_extra_file])
 
       for i in $PHP_V8JS $SEARCH_PATH ; do
+        if test -r $i/lib64/$static_link_extra_file; then
+          static_link_dir=$i/lib64
+          AC_MSG_RESULT(found in $i)
+        fi
         if test -r $i/lib/$static_link_extra_file; then
-          static_link_dir=$i
+          static_link_dir=$i/lib
           AC_MSG_RESULT(found in $i)
         fi
       done
@@ -156,7 +160,7 @@ AC_LINK_IFELSE([AC_LANG_PROGRAM([[#include <v8-debug.h>]],
         AC_MSG_ERROR([Please provide $static_link_extra_file next to the libv8.so, see README.md for details])
       fi
 
-      LDFLAGS="$LDFLAGS $static_link_dir/lib/$static_link_extra_file"
+      LDFLAGS="$LDFLAGS $static_link_dir/$static_link_extra_file"
     done
   fi