rpm: Build with 'CFLAGS=%{optflags}' and '--debug' for 'valac'

Fix 'process_error' in FastCGI: using string format without proper
parameter is an error.

Author: arteymix

data/valum.spec.in

@@ -34,7 +34,7 @@ meta-data.
 %setup -q
 
 %build
-./waf configure --prefix=%{_prefix}
+./waf configure --prefix=%{_prefix} CFLAGS="%{optflags}" VALAFLAGS='--debug'
 ./waf build
 
 %install

src/vsgi-fastcgi.vala

@@ -33,6 +33,7 @@ namespace VSGI.FastCGI {
 	private inline void process_error (global::FastCGI.Stream stream) throws IOError {
 		var error = new GLib.Error (IOError.quark (),
 		                            FileUtils.error_from_errno (stream.get_error ()), // TODO: fix and use IOError.from_errno
+		                            "%s",
 		                            strerror (stream.get_error ()));
 
 		// FastCGI error