misc: Introduce a --enable-coverage mode to build with gprof coverage

This adds a test coverage build. One can use gcov and lcov on the
resulting data afterwards to see which code paths were executed and
which were not.
diff --git a/openbsc/configure.in b/openbsc/configure.in
index f98bb70..8bbfcf8 100644
--- a/openbsc/configure.in
+++ b/openbsc/configure.in
@@ -62,6 +62,20 @@
 CFLAGS="$saved_CFLAGS"
 AC_SUBST(SYMBOL_VISIBILITY)
 
+# Coverage build taken from WebKit's configure.in
+AC_MSG_CHECKING([whether to enable code coverage support])
+AC_ARG_ENABLE(coverage,
+              AC_HELP_STRING([--enable-coverage],
+                             [enable code coverage support [default=no]]),
+              [],[enable_coverage="no"])
+AC_MSG_RESULT([$enable_coverage])
+if test "$enable_coverage" = "yes"; then
+   COVERAGE_CFLAGS="-ftest-coverage -fprofile-arcs"
+   COVERAGE_LDFLAGS="-ftest-coverage -fprofile-arcs"
+   AC_SUBST([COVERAGE_CFLAGS])
+   AC_SUBST([COVERAGE_LDFLAGS])
+fi
+
 
 dnl Generate the output
 AM_CONFIG_HEADER(bscconfig.h)