Mark compiler/version conflict for nasm

```
In file included from nasmlib/crc64.c(35):
./include/nasmlib.h(116): error: expected a ";"
  fatal_func nasm_assert_failed(const char *, int, const char *);
```

var/spack/repos/builtin/packages/nasm/package.py

@@ -22,3 +22,6 @@ class Nasm(AutotoolsPackage):
     # Fix compilation with GCC 8
     # https://bugzilla.nasm.us/show_bug.cgi?id=3392461
     patch('https://src.fedoraproject.org/rpms/nasm/raw/0cc3eb244bd971df81a7f02bc12c5ec259e1a5d6/f/0001-Remove-invalid-pure_func-qualifiers.patch', level=1, sha256='ac9f315d204afa6b99ceefa1fe46d4eed2b8a23c7315d32d33c0f378d930e950', when='@2.13.03 %gcc@8:')
+
+    # Intel 14 has immature C11 support
+    conflicts('%intel@:15', when='@2.14:')