Make building with -Werror optional.

I noticed various downstream distros patch out -Werror
for one reason or another. This adds an option to make that
easier. It is still on by default.

configure.ac

@@ -5915,6 +5915,20 @@ AC_SUBST(LCC_VERSION_STRING)
 
 AC_CONFIG_FILES(src/libcollectdclient/collectd/lcc_features.h)
 
+AM_CFLAGS="-Wall"
+AC_ARG_ENABLE([werror],
+        AS_HELP_STRING(
+                [--disable-werror],
+                [Disable -Werror @<:@default=no@:>@)]
+        )
+)
+
+if test "x$enable_werror" != "xno"
+then
+        AM_CFLAGS="$AM_CFLAGS -Werror"
+fi
+AC_SUBST([AM_CFLAGS])
+
 AC_CONFIG_FILES([Makefile src/Makefile src/daemon/Makefile src/collectd.conf src/libcollectdclient/Makefile src/libcollectdclient/libcollectdclient.pc src/liboconfig/Makefile bindings/Makefile bindings/java/Makefile])
 AC_OUTPUT
 

src/Makefile.am

@@ -6,10 +6,6 @@ SUBDIRS += daemon
 
 PLUGIN_LDFLAGS = -module -avoid-version -export-symbols-regex '\<module_register\>'
 
-if COMPILER_IS_GCC
-AM_CFLAGS = -Wall -Werror
-endif
-
 AM_CPPFLAGS = -I$(srcdir)/daemon
 AM_CPPFLAGS += -DPREFIX='"${prefix}"'
 AM_CPPFLAGS += -DCONFIGFILE='"${sysconfdir}/${PACKAGE_NAME}.conf"'

src/daemon/Makefile.am

@@ -1,7 +1,3 @@
-if COMPILER_IS_GCC
-AM_CFLAGS = -Wall -Werror
-endif
-
 AM_CPPFLAGS = -I$(top_srcdir)/src
 AM_CPPFLAGS += -DPREFIX='"${prefix}"'
 AM_CPPFLAGS += -DCONFIGFILE='"${sysconfdir}/${PACKAGE_NAME}.conf"'

src/libcollectdclient/Makefile.am

@@ -1,9 +1,5 @@
 AUTOMAKE_OPTIONS = foreign no-dependencies
 
-if COMPILER_IS_GCC
-AM_CFLAGS = -Wall -Werror
-endif
-
 pkginclude_HEADERS = collectd/client.h collectd/network.h collectd/network_buffer.h collectd/lcc_features.h
 lib_LTLIBRARIES = libcollectdclient.la
 nodist_pkgconfig_DATA = libcollectdclient.pc