libgcov is needed for gcov debug builds.

Trying without it failed on FreeBSD.  Other platforms didn't seem to
mind.

Makefile.am

@@ -7,7 +7,7 @@ memcached_SOURCES = memcached.c slabs.c slabs.h items.c items.h assoc.c assoc.h
 memcached_debug_SOURCES = $(memcached_SOURCES)
 memcached_CPPFLAGS = -DNDEBUG
 memcached_LDADD = @DTRACE_OBJ@
-memcached_debug_LDADD = @DTRACE_DEBUG_OBJ@
+memcached_debug_LDADD = @DTRACE_DEBUG_OBJ@ @PROFILER_LDFLAGS@
 memcached_DEPENDENCIES = @DTRACE_OBJ@
 memcached_debug_DEPENDENCIES = @DTRACE_DEBUG_OBJ@
 memcached_debug_CFLAGS = @PROFILER_FLAGS@

configure.ac

@@ -36,12 +36,14 @@ AC_SUBST(DTRACE_HEADER)
 AC_SUBST(DTRACE_OBJ)
 AC_SUBST(DTRACE_DEBUG_OBJ)
 AC_SUBST(DTRACEFLAGS)
+AC_SUBST(PROFILER_LDFLAGS)
 
 if test "$GCC" = "yes"
 then
    AC_PATH_PROG([PROFILER], [gcov], "no", [$PATH])
    if test "x$PROFILER" != "xno"; then
       PROFILER_FLAGS="-fprofile-arcs -ftest-coverage"
+      PROFILER_LDFLAGS="-lgcov"
    fi
 else
    AC_RUN_IFELSE(