GCC 4.6 doesn't provide std::chrono::steady_clock and GCC 4.7 doesn't provide
std::this_thread::sleep_for. I would prefer to support GCC 4.7 but I'm
reverting this since the bots are GCC 4.6.

This reverts commit c5f45495.

GCC 4.7 doesn't provide std::this_thread::sleep_for on my system.
This patch changes the tests to use a different method for wasting
cycles.

Without these, clang reorders these instructions as if they were
regular loads/stores which causes SIGILL from the kernel because
it performs all the loads before it starts testing the values.

This implementation is less likely to ICE compilers, and is more correct.
It also acts as a memory barrier which will help prevent writes to global memory
from being optimized away.

Add policy CMP0056, which honors the link flags in try_compile and
try_run. This allows for building against non-system libc++ by providing
the correct -L and rpath options in a containing project.

For example:

    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -L ${LLVM_ROOT}/lib -l c++ -l c++abi")
    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -Wl,-rpath,${LLVM_ROOT}/lib")

Add `state.SetComplexityN(state.range_x());` to documentation so that complexity is calculated correctly.

Merge branch 'added_lambdas' of git://github.com/ismaelJimenez/benchmark into ismaelJimenez-added_lambdas

* Move ComputeStats call out of the reporters

* Cleanup adjusted time calculations in reporters

* Move ComputeBigO call out of reporters

* Remove ReportComplexity interface using ReportRuns instead

* Factor out reporting of basic context information

* Attempt to fix GCC 4.6 build errors

* Move ComputeStats to complexity.cc

* Add lambda benchmarks

* Remove lambda capture since the lambda is not at a block scope

* Remove LambdaBenchmark helper since FunctionBenchmark can be used with non-capturing lambas

* Add lambda benchmarks

* Remove lambda capture since the lambda is not at a block scope

* Remove LambdaBenchmark helper since FunctionBenchmark can be used with non-capturing lambas

* Add more docs for BENCHMARK_CAPTURE.

* Fix use of misnamed parameter

* Guard BENCHMARK_CAPTURE tests against non-c++11 compilers

* Move tests out of basic_test.cc

* Add test for reporter output.

* setup err_stream tests

* Fix warnings in tests

* whitespace

* Fix build errors caused by super pedantic compilers

* Pass streams by pointer not non-const reference