package/log4cxx: fix boost-fallback (only check for boost if really needed)

- add patch 0002-boost-fallback-only-check-for-boost-if-really-needed.patch
  to check for boost if really needed (in case of legacy c++ standard < c++17)

Fixes:

  - http://autobuild.buildroot.net/results/8d49ab7cd9952f6a13bdd330e875012d0601f1d2

  -- Found Boost: .../host/x86_64-buildroot-linux-uclibc/sysroot/usr/include (found version "1.78.0") found components: thread chrono missing components: date_time atomic
  CMake Error at .../build/log4cxx-0.12.0/boost-fallback-compile-tests/CMakeFiles/CMakeTmp/CMakeLists.txt:19 (add_executable):
    Target "cmTC_aac37" links to target "Boost::date_time" but the target was
    not found.  Perhaps a find_package() call is missing for an IMPORTED
    target, or an ALIAS target is missing?

  CMake Error at .../build/log4cxx-0.12.0/boost-fallback-compile-tests/CMakeFiles/CMakeTmp/CMakeLists.txt:19 (add_executable):
    Target "cmTC_aac37" links to target "Boost::atomic" but the target was not
    found.  Perhaps a find_package() call is missing for an IMPORTED target, or
    an ALIAS target is missing?

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/log4cxx/0002-boost-fallback-only-check-for-boost-if-really-needed.patch

@@ -0,0 +1,36 @@
+From 24e7adc8d67b3c8f7d275b4f9a7e70a61b73fcd4 Mon Sep 17 00:00:00 2001
+From: Peter Seiderer <ps.report@gmx.net>
+Date: Fri, 28 Jan 2022 13:11:01 +0100
+Subject: [PATCH] boost-fallback: only check for boost if really needed
+
+- only check for boost if really needed (in case of legacy c++ standard < c++17)
+
+Signed-off-by: Peter Seiderer <ps.report@gmx.net>
+---
+ src/cmake/boost-fallback/boost-fallback.cmake | 3 +++
+ 1 file changed, 3 insertions(+)
+
+diff --git a/src/cmake/boost-fallback/boost-fallback.cmake b/src/cmake/boost-fallback/boost-fallback.cmake
+index 8285b0b9..0ecf8c6c 100644
+--- a/src/cmake/boost-fallback/boost-fallback.cmake
++++ b/src/cmake/boost-fallback/boost-fallback.cmake
+@@ -55,6 +55,8 @@ try_compile(STD_SHARED_PTR_FOUND "${CMAKE_BINARY_DIR}/boost-fallback-compile-tes
+ try_compile(STD_ATOMIC_FOUND "${CMAKE_BINARY_DIR}/boost-fallback-compile-tests"
+     "${CMAKE_CURRENT_LIST_DIR}/test-stdatomic.cpp")
+ 
++# search for boost only in case needed for legacy c++ standard < c++17
++if(NOT ${STD_THREAD_FOUND} OR NOT ${STD_MUTEX_FOUND} OR NOT ${STD_SHARED_MUTEX_FOUND} OR NOT ${STD_SHARED_PTR_FOUND} OR NOT ${STD_ATOMIC_FOUND})
+ find_package(Boost COMPONENTS thread)
+ if( ${Boost_FOUND} )
+     try_compile(Boost_SHARED_PTR_FOUND "${CMAKE_BINARY_DIR}/boost-fallback-compile-tests"
+@@ -67,6 +69,7 @@ if( ${Boost_FOUND} )
+     try_compile(Boost_ATOMIC_FOUND "${CMAKE_BINARY_DIR}/boost-fallback-compile-tests"
+         "${CMAKE_CURRENT_LIST_DIR}/test-boostatomic.cpp")
+ endif( ${Boost_FOUND} )
++endif()
+ 
+ # Link the target with the appropriate boost libraries(if required)
+ function(boostfallback_link target)
+-- 
+2.34.1
+