[trac542] include source files that depend on gtest to SOURCES only

when HAVE_GTEST is yes.  also add GTEST_INCLUDES in that case to
CPPFLAGS for libutil_unittests.

src/lib/util/unittests/Makefile.am

@@ -4,9 +4,15 @@ AM_CXXFLAGS = $(B10_CXXFLAGS)
 lib_LTLIBRARIES = libutil_unittests.la
 libutil_unittests_la_SOURCES = fork.h fork.cc resolver.h
 libutil_unittests_la_SOURCES += newhook.h newhook.cc
-libutil_unittests_la_SOURCES += run_all.h run_all.cc
 libutil_unittests_la_SOURCES += testdata.h testdata.cc
+if HAVE_GTEST
+libutil_unittests_la_SOURCES += run_all.h run_all.cc
 libutil_unittests_la_SOURCES += textdata.h
+endif
+
+if HAVE_GTEST
+libutil_unittests_la_CPPFLAGS = $(AM_CPPFLAGS) $(GTEST_INCLUDES)
+endif
 
 libutil_unittests_la_LIBADD  = $(top_builddir)/src/lib/util/libutil.la
 libutil_unittests_la_LIBADD += $(top_builddir)/src/lib/util/io/libutil_io.la