Building with GCC 4.6 fails

[hibariya]

Hello. While README.md suggests LibSass supports GCC 4.6 or higher, it seems that the current master cannot be built with GCC 4.6. I tried to build LibSass master (8e22cd4) today and got an error as follows:

$ docker run --rm -it --volume=$(pwd):/work --workdir=/work gcc:4.6 bash
root@67341c3a431e:/work# make                                                                                                                                                                 
cc -Wall -O2 -DLIBSASS_VERSION="\"3.6.1-42-g8e22\"" -I /work/include  -fPIC -c -o src/cencode.o src/cencode.c
g++ -Wall -O2 -DLIBSASS_VERSION="\"3.6.1-42-g8e22\"" -std=c++11 -I /work/include  -fPIC -c -o src/ast.o src/ast.cpp
cc1plus: error: unrecognized command line option '-std=c++11'
make: *** [src/ast.o] Error 1

According to the error message above, GCC 4.6 cannot recognize the option -std=c++11. However, even if I change the flag with -std=c++0x (by reverting c87a63e), I got another error as below:

$ docker run --rm -it --volume=$(pwd):/work --workdir=/work gcc:4.6 bash
root@8074fc389378:/work# make
cc -Wall -O2 -DLIBSASS_VERSION="\"3.6.1-43-gfab7\"" -I /work/include  -fPIC -c -o src/cencode.o src/cencode.c
g++ -Wall -O2 -DLIBSASS_VERSION="\"3.6.1-43-gfab7\"" -std=c++0x -I /work/include  -fPIC -c -o src/ast.o src/ast.cpp
In file included from src/ast_fwd_decl.hpp:9:0,
                 from src/ast.hpp:13,
                 from src/ast.cpp:5:
src/memory/SharedPtr.hpp: In copy constructor 'Sass::SharedPtr::SharedPtr(const Sass::SharedPtr&)':
src/memory/SharedPtr.hpp:116:39: error: type 'Sass::SharedPtr' is not a direct base of 'Sass::SharedPtr'
src/memory/SharedPtr.hpp: In function 'bool Sass::operator<(const Sass::SharedImpl<T1>&, const Sass::SharedImpl<T2>&)':
src/memory/SharedPtr.hpp:239:11: error: expected nested-name-specifier before 'CT'
src/memory/SharedPtr.hpp:239:11: error: 'CT' has not been declared
src/memory/SharedPtr.hpp:239:14: error: expected ';' before '=' token
src/memory/SharedPtr.hpp:239:14: error: expected primary-expression before '=' token
src/memory/SharedPtr.hpp:239:57: error: expected '(' before ';' token
src/memory/SharedPtr.hpp:240:22: error: 'CT' was not declared in this scope
src/memory/SharedPtr.hpp:240:24: error: template argument 1 is invalid
In file included from src/ast.cpp:5:0:
src/ast.hpp: At global scope:
src/ast.hpp:175:5: error: expected ';' at end of member declaration
src/ast.hpp:175:5: error: 'override' does not name a type
src/ast.hpp:175:5: error: expected ';' at end of member declaration
src/ast.hpp:175:5: error: 'override' does not name a type
src/ast.hpp:176:19: error: expected ';' at end of member declaration
src/ast.hpp:176:25: error: 'override' does not name a type
In file included from src/ast.cpp:5:0:
src/ast.hpp:495:5: error: expected ';' at end of member declaration
src/ast.hpp:495:5: error: 'override' does not name a type
src/ast.hpp:495:5: error: expected ';' at end of member declaration
src/ast.hpp:495:5: error: 'override' does not name a type
src/ast.hpp:502:21: error: expected initializer before ':' token
src/ast.cpp:953:1: error: expected '}' at end of input
src/units.hpp:11:16: warning: 'Sass::PI' defined but not used [-Wunused-variable]
make: *** [src/ast.o] Error 1

Incidentally, building with GCC 4.7 finished without errors.

[mgreter]

Seems this was broken by #2741 and #2742

[glebm]

I've updated the Readme to mention that GCC 4.7+ is required.

GCC 4.6 doesn't fully support C++11, supporting it on an ongoing basis would be quite a bit of work.

I think we should just specify "any C++11 compiler" instead of particular compiler versions (the first GCC with full C++11 support is v4.8.1, except a few libraries such as <regex>).

Incidentally, GCC 4.6.0 was released in 2011, before even VS 2013 (which I hope we can also drop support for for the next major release), and the last update to the 4.6 line was in 2013.