I think this fails to warn if users use `+tme` in an attribute or target
pragma. I tried the following testcases:
```
__attribute__((target("+tme")))
void f(void) {}
```
and:
```
#pragma GCC target ("+tme")
```
we should probably handle those cases too. Otherwise LGTM.-- https://forge.sourceware.org/gcc/gcc-TEST/pulls/186#issuecomment-6649
