[mlirc] Add missing extern C (llvm#95829)

This was missing being wrapped in extern C block.

Don't know why didn't fail elsewhere, but failed on Windows build while
linking Python libs.

Signed-off-by: Jacques Pienaar <jpienaar@google.com>

Author: jpienaar

mlir/include/mlir-c/Rewrite.h

@@ -19,6 +19,10 @@
 #include "mlir-c/Support.h"
 #include "mlir/Config/mlir-config.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 //===----------------------------------------------------------------------===//
 /// Opaque type declarations (see mlir-c/IR.h for more details).
 //===----------------------------------------------------------------------===//
@@ -57,4 +61,8 @@ mlirRewritePatternSetFromPDLPatternModule(MlirPDLPatternModule op);
 
 #undef DEFINE_C_API_STRUCT
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif // MLIR_C_REWRITE_H