What version of protobuf and what language are you using?
Version: 3.8.0
Language: C++

What operating system (Linux, Windows, ...) and version?
Windows

What runtime / compiler are you using (e.g., python version or gcc version)
msvc

What did you do?
including field_behavior.pb.h generated from https://github.com/googleapis/googleapis/blob/c9dce519127b97e866ca133a01157f4ce27dcceb/google/api/field_behavior.proto#L57 in other files results in a malformed enum definition for google::api::FieldBehavior

What did you expect to see
field_behavior.pb.h was emitted containing:

enum FieldBehavior { FIELD_BEHAVIOR_UNSPECIFIED = 0, OPTIONAL = 1, REQUIRED = 2, OUTPUT_ONLY = 3, INPUT_ONLY = 4, IMMUTABLE = 5, FieldBehavior_INT_MIN_SENTINEL_DO_NOT_USE_ = std::numeric_limits<::google::protobuf::int32>::min(), FieldBehavior_INT_MAX_SENTINEL_DO_NOT_USE_ = std::numeric_limits<::google::protobuf::int32>::max() }; 

What did you see instead?
When included after <windows.h> the resulting .i file contains:

enum FieldBehavior : int { FIELD_BEHAVIOR_UNSPECIFIED = 0, = 1, REQUIRED = 2, OUTPUT_ONLY = 3, INPUT_ONLY = 4, IMMUTABLE = 5, FieldBehavior_INT_MIN_SENTINEL_DO_NOT_USE_ = std::numeric_limits<::google::protobuf::int32>::min(), FieldBehavior_INT_MAX_SENTINEL_DO_NOT_USE_ = std::numeric_limits<::google::protobuf::int32>::max() }; 

Make sure you include information that can help us debug (full error message, exception listing, stack trace, logs).
Code example: https://godbolt.org/z/W_zBzC
The offending header is minwindef.h https://github.com/tpn/winsdk-10/blob/9b69fd26ac0c7d0b83d378dba01080e93349c2ed/Include/10.0.10240.0/shared/minwindef.h#L87
Notice it also #defines IN and OUT to empty strings as well.

Anything else we should know about your project / environment