systemc: Add Port types for initiator and target sockets.

These make it clear that a port represents a TLM socket, what direction
it faces, and what its width is.

Change-Id: Idcbea2b9b053f1e0685e011bc2c7de2468fb25b2
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/18172
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Move systemc disabling checks to SConsopts.

This will ensure that the value of USE_SYSTEMC is consistent throughout
the build. It also has the side effect that USE_SYSTEMC can be forced
to a particular value if you're confident you know what you're doing
and want to override these checks.

Change-Id: I0f2d1153245ff17ce4a828c6b7496cb9ded6bd5b
Reviewed-on: https://gem5-review.googlesource.com/c/16810
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

scons: Disable systemc on Mac OS

LLVM on Mac OS up until version 10.0.0 doesn't seem to support the
attribute for weak linking and fails to compile. Additionally, even
the basic example tests fail. Therefore, this change disables systemc
by default on Mac OS until we address these issues.

Change-Id: Iaa6360ec61317e01f4e645af8b509961b3144282
Signed-off-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/14818
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

base, systemc: Fix clang compilation

This patch is fixing the following issues:

- base: typename should be used only for types
- systemc: 'GCC_VERSION' is not defined for clang

Change-Id: I27c94445d65691a08a0a14a0ffe6b6942f6c455f
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/14976
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Disable systemc when using gcc versions older than 5.0.

These versions don't support the std::put_time function. Since versions
of gcc older than 5.0 aren't going to be supported at all in the fairly
near future, this should only be temporary. The number of people using
both systemc and older versions of gcc should be very small, or even
zero.

Change-Id: Ie9572fdf83ba9569df6bc0457c98d86565dcdcd8
Reviewed-on: https://gem5-review.googlesource.com/c/14755
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Put systemc headers in the include path when supported.

When the native systemc API support is built in, put the systemc and
systemc.h header files in the include path so they can be used as
normal. We don't want any external systemc headers being included and
getting mixed in with our local ones.

Change-Id: I5fc01ff5f069cfadb7c19a9dead13e7ce7272976
Reviewed-on: https://gem5-review.googlesource.com/c/14397
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Gabe Black <gabeblack@google.com>