protoc-c: fix shared lib build on windows, migrate from Travis CI to GitHub Actions

We are now able to build against Mac and Windows.
But, mainly, see:
https://blog.travis-ci.com/2020-11-02-travis-ci-new-billing
https://docs.travis-ci.com/user/migrate/open-source-on-travis-ci-com/

Matches protobuf default behavior:
https://github.com/protocolbuffers/protobuf/tree/master/cmake#dlls-vs-static-linking

Bump min cmake version to use Protobuf_USE_STATIC_LIBS:
https://cmake.org/cmake/help/latest/module/FindProtobuf.html

MSVC has issues importing protobuf_c_empty_string from the DLL and using
it in initializers, resulting in errors like when linking against
protobuf-c.dll:
  test-proto3.pb-c.c(13): error C2099: initializer is not a constant
  test-proto3.pb-c.c(19): error C2440: 'initializing': cannot convert from 'void *' to 'Foo__Person__PhoneType'

Work around the issue by not exporting protobuf_c_empty string and
defining it as static const char[] in the protobuf-c.h file itself. This
change only applies to _WIN32 shared library builds.

This reverts commit 4c8043d0.

Fixes #458
Signed-off-by: Ilya Lipnitskiy <ilya.lipnitskiy@gmail.com>

Avoid "unused function parameter" compiler warning

fix invalid unsigned arithmetic.

Install debug symbols alongside the protobuf-c.lib

A user of the protobuf-c library is confronted with MSVC warnings about missing
PDB if the library happens to be built/configured using the CMAKE_BUILD_TYPE
"Debug" or "RelWithDebInfo". This commit deals away with the warning by
installing the "protobuf-c.pdb" alongside the lib. The .pdb is installed only
if it exists. Configuring "Release" or building under Linux won't produce and
won't install the PDB.

Updated the generator to fully qualify std::string

The protobuf common.h header currently has a "using std::string;"
statement that pulls std::string into the google::protobuf namespace:
https://github.com/protocolbuffers/protobuf/blob/ce66f6047db44df3234bccd6fcf468bccc14a760/src/google/protobuf/stubs/common.h#L195

I plan to delete that line soon. To keep protobuf-c working, this commit
updates the generator to fully qualify std::string.

Travis CI: Test on other platforms

Travis CI now supports testing on arm64, ppc64le and s390x. It would
be nice to test on them.
Signed-off-by: Daniel Axtens <dja@axtens.net>

Bionic contains more recent compilers, which are required to have
the sanitisers work under s390x.

While we're at it, the 'sudo' key is deprecated, so remove it:

https://blog.travis-ci.com/2018-11-19-required-linux-infrastructure-migration

(It used to be used to mark VM vs docker container infrastructure,
but currently all amd64 builds run on VMs and all other archs run
inside LXD containers.)
Signed-off-by: Daniel Axtens <dja@axtens.net>

Pack nested messages inline

protoc-c: Remove leading underscores from structs

protobuf-c.c: Cast %lu args to unsigned long int

Standardize pkg-config for use by autotools and cmake, fix cmake tests

protobuf-c.h: Fix Windows DLL export (Fixes #331)

c_message.cc: Resolve name conflict (Fixes #389)

Signed-off-by: Markus Engel <engel@sero-systems.de>

Fixes #188.

Implements suggested fix from the issue:
The struct tag namespace is different from the type namespace. Use the
same symbol names (i.e. without leading underscores) in every namespace.

Also use BUILD_TESTS instead of CMAKE_BUILD_TYPE in other places in the
file.

Resolves an ambiguity that %zu was meant to address, since %zu is not
present on all platforms.

Fixes #357.

protobuf_c_empty_string is used in generated .pb-c.{c,h} files so it
should be exported properly.

lib.protobuf-c.io is no longer reachable.

-lpthread was missing from the linker command line. See
https://github.com/protocolbuffers/protobuf/issues/5107 for more
details.

.travis.yml: Run CMake debug build for verification

PACKAGE_DESCRIPTION is defined in configure.ac. PACKAGE_NAME,
PACKAGE_VERSION, and PACKAGE_URL come from AC_INIT.

This change will ensure that libprotobuf-c.pc.in could also be used by
CMake.

Bump version to 1.3.3