package/protobuf: needs gcc >= 4.5

package/protobuf: needs gcc >= 4.5

Even with an upstream patch from protobuf v3.3 [1], the build fail with another issue:

In file included from google/protobuf/dynamic_message.cc:80:
./google/protobuf/map_field.h: In member function 'void google::protobuf::internal::MapField<Key, T, key_wire_type, value_wire_type, default_enum_value>::Swap(google::protobuf::internal::MapFieldLite<Key, T, kKeyFieldType, kValueFieldType, default_enum_value>*)':
./google/protobuf/map_field.h:139: error: object missing in reference to 'google::protobuf::internal::MapFieldBase::repeated_field_'
./google/protobuf/map_field_inl.h:342: error: from this location
./google/protobuf/map_field.h:150: error: object missing in reference to 'google::protobuf::internal::MapFieldBase::state_'
./google/protobuf/map_field_inl.h:344: error: from this location

Add a dependency on gcc >= 4.5.

[1] https://github.com/google/protobuf/commit/a83ac8663fb8042a881bc60b12a8bd3a0c03a3ff

Fixes:
http://autobuild.buildroot.org/results/77d/77dbb6bbbc0ea9e9bcdd22b10011ef9728c20d54
http://autobuild.buildroot.org/results/21f/21f5e1ea4f37e1d174604d6da78c0e916c89f1e3
http://autobuild.buildroot.org/results/24e/24e880086c87d40b5d79a90d805acc75b33d484c

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Cc: Mario J. Rugiero <mrugiero@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>