Fix strict mode errors in built-ins/Math

test/built-ins/Math/E/S15.8.1.1_A2.js

test/built-ins/Math/LN10/S15.8.1.2_A2.js

test/built-ins/Math/LN2/S15.8.1.3_A2.js

test/built-ins/Math/LOG10E/S15.8.1.5_A2.js

test/built-ins/Math/LOG2E/S15.8.1.4_A2.js

test/built-ins/Math/PI/S15.8.1.6_A2.js

test/built-ins/Math/SQRT1_2/S15.8.1.7_A2.js

test/built-ins/Math/SQRT2/S15.8.1.8_A2.js

test/built-ins/Math/acos/S15.8.2.2_A5.js

test/built-ins/Math/asin/S15.8.2.3_A6.js

test/built-ins/Math/atan/S15.8.2.4_A6.js

test/built-ins/Math/atan2/S15.8.2.5_A1.js

test/built-ins/Math/atan2/S15.8.2.5_A10.js

test/built-ins/Math/atan2/S15.8.2.5_A11.js

test/built-ins/Math/atan2/S15.8.2.5_A12.js

test/built-ins/Math/atan2/S15.8.2.5_A13.js

test/built-ins/Math/atan2/S15.8.2.5_A14.js

test/built-ins/Math/atan2/S15.8.2.5_A15.js

test/built-ins/Math/atan2/S15.8.2.5_A16.js

test/built-ins/Math/atan2/S15.8.2.5_A17.js