ETL: requires C++11

[chrstphrchvz (Christopher Chavez)]

Build fails at least on ​10.6:

checking whether /usr/bin/g++-4.2 supports C++11 features by default... no
checking whether /usr/bin/g++-4.2 supports C++11 features with -std=c++11... no
checking whether /usr/bin/g++-4.2 supports C++11 features with -std=c++0x... no
checking whether /usr/bin/g++-4.2 supports C++11 features with +std=c++11... no
checking whether /usr/bin/g++-4.2 supports C++11 features with -h std=c++11... no
configure: error: *** A compiler with support for C++11 language features is required.

The port should specify compiler.cxx_standard 2011. Not sure if this should also be specified for dependents synfig/synfigstudio.

There is usage of depends_build rather than depends_build-append—would this interfere with dependencies added from compiler selection?

(I personally do not use this port.)

[ryandesign (Ryan Carsten Schmidt)]

In 0b3503e485dd3cd6edf564a1ec11ce8800a6209c/macports-ports (master):

ETL: Requires C++11

See: #61578

[ryandesign (Ryan Carsten Schmidt)]

In ead01aed56ef660e893d7b67d30c0b16b785c774/macports-ports (master):

synfig: Requires C++11

See: #61578

[ryandesign (Ryan Carsten Schmidt)]

In 3833ce93481f3e294e892b277cd6074040833a8e/macports-ports (master):

synfigstudio: Requires C++11

Closes: #61578