package/rpi-userland: fix build without libexecinfo

Fix the following build failure without libexecinfo raised since commit
66d7d3bec341188bcfd83fa70b44dd62e0073431:

CMake Error: The following variables are used in this project, but they are set to NOTFOUND.
Please set them or make sure they are set and tested correctly in the CMake files:
EXECINFO_LIBRARY
    linked by target "vcos" in directory /home/buildroot/autobuild/run/instance-1/output-1/build/rpi-userland-14b90ff9d9f031391a299e6e006965d02bfd1bb1/interface/vcos/pthreads

Fixes:
 - http://autobuild.buildroot.org/results/0b4b20e4eed1ed5120f22d29fc24038f268e6cc6

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/rpi-userland/0006-interface-vcos-pthreads-CMakeLists.txt-fix-build-wit.patch

@@ -1,4 +1,4 @@
-From 220c37b496f5c883bbfa955ee7fee471e41c34d4 Mon Sep 17 00:00:00 2001
+From c8270cea98bcce0d22ddc8e2f86eae2c9989efd4 Mon Sep 17 00:00:00 2001
 From: Fabrice Fontaine <fontaine.fabrice@gmail.com>
 Date: Fri, 25 Feb 2022 19:21:06 +0100
 Subject: [PATCH] interface/vcos/pthreads/CMakeLists.txt: fix build with
@@ -20,7 +20,7 @@ Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
  1 file changed, 4 insertions(+), 2 deletions(-)
 
 diff --git a/interface/vcos/pthreads/CMakeLists.txt b/interface/vcos/pthreads/CMakeLists.txt
-index 1d81ca3..43aca03 100644
+index 1d81ca3..100207f 100644
 --- a/interface/vcos/pthreads/CMakeLists.txt
 +++ b/interface/vcos/pthreads/CMakeLists.txt
 @@ -33,12 +33,14 @@ set (SOURCES
@@ -32,11 +32,11 @@ index 1d81ca3..43aca03 100644
  if (VCOS_PTHREADS_BUILD_SHARED)
     add_library (vcos SHARED ${SOURCES})
 -   target_link_libraries (vcos pthread dl rt)
-+   target_link_libraries (vcos pthread dl rt ${EXECINFO_LIBRARY})
++   target_link_libraries (vcos pthread dl rt $<$<BOOL:${EXECINFO_LIBRARY}>:${EXECINFO_LIBRARY}>)
  else ()
     add_library (vcos ${SOURCES})
 -   target_link_libraries (vcos pthread rt)
-+   target_link_libraries (vcos pthread rt ${EXECINFO_LIBRARY})
++   target_link_libraries (vcos pthread rt $<$<BOOL:${EXECINFO_LIBRARY}>:${EXECINFO_LIBRARY}>)
  endif ()