[oe] [PATCH][meta-oe] glog: fix libunwind search in components which depend on glog

[Martin Jansa]

* libunwind is not found when using find_package(glog) from some
  other recipe, without this change it fails with:

CMake Error at /OE/build/owpb/webos-ports/tmp-glibc/work/tissot-webos-linux/mtp-server/0.0.3+gitrAUTOINC+6159f1a143-r0/recipe-sysroot-native/usr/share/cmake-3.12/Modules/CMakeFindDependencyMacro.cmake:48 (find_package):
  By not providing "FindLibunwind.cmake" in CMAKE_MODULE_PATH this project
  has asked CMake to find a package configuration file provided by
  "Libunwind", but CMake did not find one.

  Could not find a package configuration file provided by "Libunwind" with
  any of the following names:

    LibunwindConfig.cmake
    libunwind-config.cmake

  Add the installation prefix of "Libunwind" to CMAKE_PREFIX_PATH or set
  "Libunwind_DIR" to a directory containing one of the above files.  If
  "Libunwind" provides a separate development package or SDK, be sure it has
  been installed.
Call Stack (most recent call first):
  /OE/build/owpb/webos-ports/tmp-glibc/work/tissot-webos-linux/mtp-server/0.0.3+gitrAUTOINC+6159f1a143-r0/recipe-sysroot/usr/lib/cmake/glog/glog-config.cmake:31 (find_dependency)
  CMakeLists.txt:17 (find_package)

-- Configuring incomplete, errors occurred!

* this might help others when upgrading to thud which has newer glog:

mtp-server in meta-luneos layer is the only user of glog I could find
in public layers, it was failing to build with 0.3.5 version of glog
(and building fine with 0.3.4 glog which was built with autotools
instead of cmake and provided pkg-config instead of glog-config.cmake)

First part is relatively simple, update CMakeLists.txt to use cmake
machinery instead of pkg-config:

-pkg_check_modules(GLOG REQUIRED libglog)
+find_package(glog 0.3.5 REQUIRED)

and update the use of GLOG_* variables, e.g.:
-  ${GLOG_LIBRARIES}
+  glog::glog

interestingly glog::glog passes the glog library with whole path, in my
case:
  /OE/build/owpb/webos-ports/tmp-glibc/work/tissot-webos-linux/ \
  mtp-server/0.0.3+gitrAUTOINC+6159f1a143-r0/recipe-sysroot/usr/lib/ \
  libglog.so.0.3.5 -lunwind -lunwind-aarch64
instead of just -lglog -unwind -lunwind-aarch64 which would work as
well, because sysroot is configured correctly elsewhere.

I'm not sure if this is really expected behavior of glog::glog or
another bug in glog-config.cmake.

Signed-off-by: Martin Jansa <Martin.Jansa at gmail.com>
---
 .../0002-Find-Libunwind-during-configure.patch    | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/meta-oe/recipes-support/glog/glog/0002-Find-Libunwind-during-configure.patch b/meta-oe/recipes-support/glog/glog/0002-Find-Libunwind-during-configure.patch
index 15cf67fd2e..4d7642a907 100644
--- a/meta-oe/recipes-support/glog/glog/0002-Find-Libunwind-during-configure.patch
+++ b/meta-oe/recipes-support/glog/glog/0002-Find-Libunwind-during-configure.patch
@@ -109,12 +109,21 @@ diff -uNr a/CMakeLists.txt b/CMakeLists.txt
  
  install (EXPORT glog-targets NAMESPACE glog:: DESTINATION lib/cmake/glog)
 diff -uNr a/glog-config.cmake.in b/glog-config.cmake.in
---- a/glog-config.cmake.in	2018-11-20 15:49:07.576278417 +0100
-+++ b/glog-config.cmake.in	2018-11-20 15:52:32.330418489 +0100
-@@ -4,4 +4,6 @@
+--- a/glog-config.cmake.in	2018-11-02 14:02:21.784835854 +0100
++++ b/glog-config.cmake.in	2018-11-02 14:03:16.796935594 +0100
+@@ -4,4 +4,15 @@
  
  @gflags_DEPENDENCY@
  
++# Record the state of the CMake module path when this script was
++# called so that we can ensure that we leave it in the same state on
++# exit as it was on entry, but modify it locally.
++set(UNWIND_CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH})
++
++set(CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}")
 +find_dependency (Libunwind)
++
++# Restore original module path
++set(CMAKE_MODULE_PATH "${UNWIND_CMAKE_MODULE_PATH}")
 +
  include ("${CMAKE_CURRENT_LIST_DIR}/glog-targets.cmake")
-- 
2.17.1