build: Do not require find_package(dpkd) when using seastar

dpdk is included to within seastar, accordingly it should not be
required to have dpdk package available when using seastar as
dependency.

This fixes build failures when attempting to use seastar from a custom
install prefix.

Author: p12tic

Diff for: CMakeLists.txt

@@ -396,7 +396,7 @@ set (Seastar_GEN_BINARY_DIR ${Seastar_BINARY_DIR}/gen)
 #
 
 include (SeastarDependencies)
-seastar_find_dependencies ()
+seastar_find_dependencies (BUILD)
 
 # Private build dependencies not visible to consumers
 find_package (ragel 6.10 REQUIRED)

Diff for: cmake/SeastarDependencies.cmake

@@ -75,6 +75,8 @@ endmacro ()
 # with the corresponding configuration for each 3rd-party dependency.
 #
 macro (seastar_find_dependencies)
+  cmake_parse_arguments (args "BUILD" "" "" ${ARGN})
+
   #
   # List of Seastar dependencies that is meant to be used
   # both in Seastar configuration and by clients which
@@ -84,7 +86,6 @@ macro (seastar_find_dependencies)
     # Public dependencies.
     Boost
     c-ares
-    dpdk # No version information published.
     fmt
     lz4
     # Private and private/public dependencies.
@@ -103,6 +104,12 @@ macro (seastar_find_dependencies)
     ucontext
     yaml-cpp)
 
+  # Only expose dpdk dependency during build. Since dpdk is included to within seastar library,
+  # there is no need to force it to be discoverable via find_package().
+  if (args_BUILD)
+    list (APPEND _seastar_all_dependencies dpdk)
+  endif()
+
   # Arguments to `find_package` for each 3rd-party dependency.
   # Note that the version specification is a "minimal" version requirement.