build: coverage: disable branch coverage generation to avoid hangs in gcov

I have seen hangs with gcov on Jenkins and locally where the processing just
keeps spinning in an infinite loop. From what I have found out this boils down
to using gcov --all-blocks which is what lcov does with branch coverage enabled.
It is supposed to be fixed in gcc 4.8+ but I see this here with 5.3.1. So its
either a regression or not completely fixed. In any case we will ignore branch
coverage for now. I hoped it would work well but it did only for a while and
having line and function coverage is better than having nothing.

.lcov-config

@@ -1,3 +1 @@
 geninfo_auto_base=1
-lcov_branch_coverage=1
-genhtml_branch_coverage=1

Makefile.am

@@ -451,16 +451,16 @@ lcov-reset:
 
 lcov-baseline:
 	$(MKDIR_P) $(top_builddir)/coverage
-	lcov --capture --initial --compat-libtool --no-external --output-file $(top_builddir)/coverage/coverage-baseline.info --directory $(top_builddir) --config-file .lcov-config --rc lcov_branch_coverage=1
+	lcov --capture --initial --compat-libtool --no-external --output-file $(top_builddir)/coverage/coverage-baseline.info --directory $(top_builddir) --config-file .lcov-config
 
 lcov-report:
-	lcov --capture --compat-libtool --no-external --output-file $(top_builddir)/coverage/coverage-check.info --directory $(top_builddir) --config-file .lcov-config --rc lcov_branch_coverage=1
-	lcov --no-external --compat-libtool --add-tracefile $(top_builddir)/coverage/coverage-baseline.info --add-tracefile $(top_builddir)/coverage/coverage-check.info --output-file $(top_builddir)/coverage/coverage.info --config-file .lcov-config --rc lcov_branch_coverage=1
-	lcov --no-external --compat-libtool --remove $(top_builddir)/coverage/coverage.info '*.h' --output-file $(top_builddir)/coverage/coverage.cleaned.info --config-file .lcov-config --rc lcov_branch_coverage=1
-	lcov --no-external --compat-libtool --remove $(top_builddir)/coverage/coverage.cleaned.info '*/tests/*' --output-file $(top_builddir)/coverage/coverage.cleaned2.info --config-file .lcov-config --rc lcov_branch_coverage=1
-	lcov --no-external --compat-libtool --remove $(top_builddir)/coverage/coverage.cleaned2.info '*NONE*' --output-file $(top_builddir)/coverage/coverage.cleaned3.info --config-file .lcov-config --rc lcov_branch_coverage=1
-	lcov --no-external --compat-libtool --remove $(top_builddir)/coverage/coverage.cleaned3.info '*/doc/*' --output-file $(top_builddir)/coverage/coverage.cleaned4.info --config-file .lcov-config --rc lcov_branch_coverage=1
-	lcov --no-external --compat-libtool --remove $(top_builddir)/coverage/coverage.cleaned4.info '*usr/include*' --output-file $(top_builddir)/coverage/coverage.cleaned5.info --config-file .lcov-config --rc lcov_branch_coverage=1
+	lcov --capture --compat-libtool --no-external --output-file $(top_builddir)/coverage/coverage-check.info --directory $(top_builddir) --config-file .lcov-config
+	lcov --no-external --compat-libtool --add-tracefile $(top_builddir)/coverage/coverage-baseline.info --add-tracefile $(top_builddir)/coverage/coverage-check.info --output-file $(top_builddir)/coverage/coverage.info --config-file .lcov-config
+	lcov --no-external --compat-libtool --remove $(top_builddir)/coverage/coverage.info '*.h' --output-file $(top_builddir)/coverage/coverage.cleaned.info --config-file .lcov-config
+	lcov --no-external --compat-libtool --remove $(top_builddir)/coverage/coverage.cleaned.info '*/tests/*' --output-file $(top_builddir)/coverage/coverage.cleaned2.info --config-file .lcov-config
+	lcov --no-external --compat-libtool --remove $(top_builddir)/coverage/coverage.cleaned2.info '*NONE*' --output-file $(top_builddir)/coverage/coverage.cleaned3.info --config-file .lcov-config
+	lcov --no-external --compat-libtool --remove $(top_builddir)/coverage/coverage.cleaned3.info '*/doc/*' --output-file $(top_builddir)/coverage/coverage.cleaned4.info --config-file .lcov-config
+	lcov --no-external --compat-libtool --remove $(top_builddir)/coverage/coverage.cleaned4.info '*usr/include*' --output-file $(top_builddir)/coverage/coverage.cleaned5.info --config-file .lcov-config
 	genhtml --config-file .lcov-config --legend -t "$(PACKAGE_STRING)" -o $(top_builddir)/coverage/html $(top_builddir)/coverage/coverage.cleaned5.info
 	@echo "Coverage Report at $(top_builddir)/coverage/html"