[mlir-c] Avoid compiler warning

[jpienaar]

Summary

Setting visibility & static leads to warning about attribute being
ignored. Remove static as I believe this is desired to be exported.

[mehdi_amini]

Shouldn't we remove the MLIR_CAPI_EXPORTED instead?

(Also, from what I read online: "In C, inline functions are treated by default as having static linkage")

[jpienaar]

I was expecting mlirTypeIDIsNull exported to be able to use it from generated library, but you are correct that inline has effect here similar to static wrt symbol exported, so inlining and not exporting SGTM

[jpienaar]

Removing export instead.

[jpienaar]

Fix incorrectly uploaded test case

[mehdi_amini]

I was expecting mlirTypeIDIsNull exported to be able to use it from generated library

You can use it from anywhere, it will just be with the user and not really part of the library ABI.
(so it only limits your ability to dlopen/dlsym find it)

mlir/include/mlir-c/IR.h

 /// Gets the string value of the identifier.
 MLIR_CAPI_EXPORTED MlirStringRef mlirIdentifierStr(MlirIdentifier ident);
 
 //===----------------------------------------------------------------------===//
 // TypeID API.
 //===----------------------------------------------------------------------===//
 
 /// Checks whether a type id is null.
-MLIR_CAPI_EXPORTED static inline bool mlirTypeIDIsNull(MlirTypeID typeID) {
-  return !typeID.ptr;
-}
+static inline bool mlirTypeIDIsNull(MlirTypeID typeID) { return !typeID.ptr; }
 
 /// Checks if two type ids are equal.
 MLIR_CAPI_EXPORTED bool mlirTypeIDEqual(MlirTypeID typeID1, MlirTypeID typeID2);
 
 /// Returns the hash value of the type id.
 MLIR_CAPI_EXPORTED size_t mlirTypeIDHashValue(MlirTypeID typeID);
 
 #ifdef __cplusplus
 }
 #endif
 
 #endif // MLIR_C_IR_H