[Buildroot] [git commit] package/gerbera: fix build with -Os and gcc 9 or 10

commit: https://git.buildroot.net/buildroot/commit/?id=c68efce50c88f6d5f2fa548b4082e423d1828991
branch: https://git.buildroot.net/buildroot/commit/?id=refs/heads/master

For an unknown reason, gerbera fails to build with -Os and gcc 9 or 10
since bump to version 1.8.0 in commit 8974596836945eada8e162844fb87f88adec9100:

[100%] Linking CXX executable gerbera
/home/giuliobenetti/autobuild/run/instance-3/output-1/host/opt/ext-toolchain/bin/../lib/gcc/x86_64-buildroot-linux-gnu/10.2.0/../../../../x86_64-buildroot-linux-gnu/bin/ld: liblibgerbera.a(content_manager.cc.o): in function `ContentManager::_rescanDirectory(std::shared_ptr<AutoscanDirectory>&, int, std::shared_ptr<GenericTask> const&)':
content_manager.cc:(.text+0xb53b): undefined reference to `std::__shared_ptr<std::filesystem::__cxx11::_Dir, (__gnu_cxx::_Lock_policy)2>::swap(std::__shared_ptr<std::filesystem::__cxx11::_Dir, (__gnu_cxx::_Lock_policy)2>&)'
collect2: error: ld returned 1 exit status

A similar build failure has been reported as gcc bug 91067:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91067

But this bug has been fixed since gcc 9.3 and 10.1 and build failures
are raised with gcc 10.2

To fix this build failure, set optimisation to -O2 if needed

Fixes:
 - http://autobuild.buildroot.org/results/a4ee8ad7ff93939716673b611c7cc3f68dafa3d0

Signed-off-by: Fabrice Fontaine <redacted>
Signed-off-by: Yann E. MORIN <redacted>
---
 package/gerbera/gerbera.mk | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/package/gerbera/gerbera.mk b/package/gerbera/gerbera.mk
index 73917c7721..9627209d60 100644
--- a/package/gerbera/gerbera.mk
+++ b/package/gerbera/gerbera.mk

@@ -18,6 +18,10 @@ GERBERA_DEPENDENCIES = \
 	zlib
 GERBERA_CONF_OPTS = -DWITH_DEBUG=OFF
 
+ifeq ($(BR2_TOOLCHAIN_GCC_AT_LEAST_9)$(BR2_OPTIMIZE_S),yy)
+GERBERA_CONF_OPTS += -DCMAKE_CXX_FLAGS="$(TARGET_CXXFLAGS) -O2"
+endif
+
 # Uses __atomic_fetch_add_4
 ifeq ($(BR2_TOOLCHAIN_HAS_LIBATOMIC),y)
 GERBERA_CONF_OPTS += -DCMAKE_EXE_LINKER_FLAGS=-latomic