more small build tweaks. use mkdtemp if available

src/mk/FreeBSD

@@ -2,7 +2,8 @@ CXXFLAGS = -pthread -Wall -Wno-unused-variable -g \
 	 -I. -I../index -I../utils -I../common \
 	 -I../unac -I../bincimapmime -I/usr/local/include  \
 	 \
-	 -DHAVE_VASPRINTF=1
+	 -DHAVE_VASPRINTF=1 \
+	 -DHAVE_MKDTEMP=1
 
 LIBXAPIAN = -L/usr/local/lib -lxapian
 LIBICONV =  -L/usr/local/lib -liconv

src/mk/Linux

@@ -1,7 +1,8 @@
 CXXFLAGS = -Wall -g -I. -I../index -I../utils -I../common \
 	 -I../unac -I../bincimapmime -I/usr/local/include \
-	 \
-	 -DHAVE_VASPRINTF=1 -D_GNU_SOURCE
+	 -D_GNU_SOURCE \
+	 -DHAVE_VASPRINTF=1 \
+	 -DHAVE_MKDTEMP=1
 
 LIBXAPIAN = -L/usr/local/lib -lxapian
 LIBICONV =