UPSTREAM: meson.build: change operator combining bools from + to and

upstream meson stopped allowing combining boolean with the plus
operator, and now requires using the logical and operator

reference:
mesonbuild/meson@43302d3

Fixes: #20632

BUG=b:221852556
TEST=emerge-$BOARD systemd-tmpfiles

Change-Id: I537309e9dbfc9181bf67b523f31638518dece59d
diff --git a/meson.build b/meson.build
index f406d59..f172c94 100644
--- a/meson.build
+++ b/meson.build
@@ -43,7 +43,7 @@
 
 want_ossfuzz = get_option('oss-fuzz')
 want_libfuzzer = get_option('llvm-fuzz')
-if want_ossfuzz + want_libfuzzer > 1
+if want_ossfuzz and want_libfuzzer
         error('only one of oss-fuzz or llvm-fuzz can be specified')
 endif