GCC 4.8 arm EIGEN_OPTIMIZATION_BARRIER fix (#2315). GCC 4.8 doesn't seem to like the `g` register constraint, failing to compile with "error: 'asm' operand requires impossible reload". Tested `r` instead, and that seems to work, even with latest compilers. Also fixed some minor macro issues to eliminate warnings on armv7. Fixes #2315.
Eigen is a C++ template library for linear algebra: matrices, vectors, numerical solvers, and related algorithms.
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