Mark compiler/version conflict for bison

```
In file included from /tmp/s3j/spack-stage/spack-stage-bison-3.4.2-
uzjszv4owvqsymjpxtxvvegfavc6k5my/spack-src/lib/quotearg.c(33):
/tmp/s3j/spack-stage/spack-stage-bison-3.4.2-uzjszv4owvqsymjpxtxvvegfavc6k5my/spack-src/lib/
xalloc.h(51): warning spack#303: explicit type is missing ("int" assumed)
  extern _Noreturn void xalloc_die (void);
```

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

@@ -31,6 +31,9 @@ class Bison(AutotoolsPackage):
 
     patch('pgi.patch', when='@3.0.4')
 
+    # Intel 14 has immature C11 support
+    conflicts('%intel@:15', when='@3.4.2:')
+
     if sys.platform == 'darwin' and macos_version() >= Version('10.13'):
         patch('secure_snprintf.patch', level=0, when='@3.0.4')