Pass gb_VISIBILITY_FLAGS into external/breakpad

...to avoid UBSan (on Linux) reporting a ODR violation between
google_breakpad::MinidumpDescriptor::kMicrodumpOnConsole (workdir/
UnpackedTarball/breakpad/src/client/linux/handler/minidump_descriptor.cc)
defined in both the crashreport and sofficeapp dynamic libs.

Change-Id: I686a6e2041c70f0aa17a774d705dc71d95d20183
diff --git a/external/breakpad/ExternalProject_breakpad.mk b/external/breakpad/ExternalProject_breakpad.mk
index 10fa6ce..f95b4b2 100644
--- a/external/breakpad/ExternalProject_breakpad.mk
+++ b/external/breakpad/ExternalProject_breakpad.mk
@@ -20,7 +20,7 @@ else # !ifeq($(COM),MSC)

$(call gb_ExternalProject_get_state_target,breakpad,build) :
	$(call gb_ExternalProject_run,build,\
		CXX_FLAGS="-O2" ./configure \
		./configure CXXFLAGS="-O2 $(gb_VISIBILITY_FLAGS)" \
		&& $(MAKE) \
	)