nasm: Try to add skip test clause

Author: amyspark

test cases/nasm/3 nasm only/meson.build

@@ -1,4 +1,8 @@
-project('nasm only', 'nasm')
+project('nasm only')
+
+if not add_languages('nasm', required: false)
+  error('MESON_SKIP_TEST: nasm not found')
+endif
 
 sources = files('dummy.asm')