Add option to disable building unit tests in Meson build file.

meson.build

@@ -14,4 +14,6 @@ project(
 )
 
 subdir('src/catch2')
-subdir('tests')
+if get_option('tests')
+  subdir('tests')
+endif

meson_options.txt

@@ -0,0 +1 @@
+option('tests', type: 'boolean', value: true, description: 'Build the unit tests')