Separate math/big test.

tests/core/math/big/build.bat

@@ -0,0 +1,13 @@
+@echo off
+rem math/big tests
+set PATH_TO_ODIN==..\..\..\..\odin
+set TEST_ARGS=-fast-tests
+set TEST_ARGS=
+set OUT_NAME=math_big_test_library
+set COMMON=-build-mode:shared -show-timings -no-bounds-check -define:MATH_BIG_EXE=false -vet -strict-style
+echo ---
+echo Running core:math/big tests
+echo ---
+
+%PATH_TO_ODIN% build . %COMMON% -o:speed -out:%OUT_NAME%
+python3 test.py %TEST_ARGS%