gmtl: Fix build issues

[ryandesign]

Description

Add patches to fix build failures when using clang, when using the latest version of scons, when scons is using python 3, and to prevent the creation of the unwanted file gmtl-0.6.1.tar.gz and to install the file gmtl.pc.

Add runtime dependencies on flagpoll and python which are used by gmtl-config. flagpoll is currently incompatible with python 3 and uses python27 so use the same python here to reduce the number of pythons a user needs to install.

Specify absolute path to scons.

Specify prefix at build time so that build output does not give the erroneous impression that files will be installed in /usr/local.

Specify empty directories for Boost and CppUnit at build time so that any Boost or CppUnit that might be installed in /usr/local is not inadvertently used.

No need to specify destroot.cmd or destroot.target; the defaults work.

Add modeline.

Modernize checksums.

Set platforms to any and set supported_archs to noarch because this port doesn't install anything architecture- or OS-specific.

Add GitHub handle to maintainers line.

Install documentation files.

Indicate license. The software claims to be licensed LGPL-2.1+ but there is also a license addendum that imposes additional restrictions and the LGPL does not permit the imposition of additional restrictions.

Rewrite master_sites to avoid redirects.

Closes: https://trac.macports.org/ticket/57421

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@mccdo as with #17916 I've added your GitHub handle to the maintainers line. If you don't want to maintain this port anymore let us know and we'll remove you. If the email address needs updating let us know the new address. If you allow others to make changes to this port without consulting you let us know and we'll add openmaintainer.

I did already make one change to this port without consulting you — d4a979b — apologies. This was based on the fact that you had not responded to the ticket that this PR fixes for over four years and the port had not been installable at all since Xcode 5 was released almost ten years ago.

Type(s)

• bugfix
• enhancement
• security fix

Tested on

macOS 12.3.1 21E258 x86_64
Xcode 13.2.1 13C100

Verification

Have you

• followed our Commit Message Guidelines?
• squashed and minimized your commits?
• checked that there aren't other open pull requests for the same change?
• referenced existing tickets on Trac with full URL?
• checked your Portfile with port lint --nitpick?
• tried existing tests with sudo port test?
• tried a full install with sudo port -vst install?
• tested basic functionality of all binary files?
• checked that the Portfile's most important variants haven't been broken?