lots of miscellaneous things all in one big commit

* add `@compileLog(...)` builtin function
   - Helps debug code running at compile time
   - See #240
 * fix crash when there is an error on the start value of a slice
 * add implicit cast from int and float types to int and float
   literals if the value is known at compile time
 * make array concatenation work with slices in addition to
   arrays and c string literals
 * fix compile error message for something not having field access
 * fix crash when `@setDebugSafety()` was called from a
   function being evaluated at compile-time
 * fix compile-time evaluation of overflow math builtins.
 * avoid debug safety panic handler in builtin.o and compiler_rt.o
   since we use no debug safety in these modules anyway
 * add compiler_rt functions for division on ARM
   - Closes #254
 * move default panic handler to std.debug so users can
   call it manually
 * std.io.printf supports a width in the format specifier

src/codegen.cpp

@@ -2377,6 +2377,7 @@ static LLVMValueRef ir_render_instruction(CodeGen *g, IrExecutable *executable,
         case IrInstructionIdMinValue:
         case IrInstructionIdMaxValue:
         case IrInstructionIdCompileErr:
+        case IrInstructionIdCompileLog:
         case IrInstructionIdArrayLen:
         case IrInstructionIdImport:
         case IrInstructionIdCImport:
@@ -3791,6 +3792,7 @@ static void define_builtin_fns(CodeGen *g) {
     create_builtin_fn(g, BuiltinFnIdDivExact, "divExact", 2);
     create_builtin_fn(g, BuiltinFnIdTruncate, "truncate", 2);
     create_builtin_fn(g, BuiltinFnIdCompileErr, "compileError", 1);
+    create_builtin_fn(g, BuiltinFnIdCompileLog, "compileLog", SIZE_MAX);
     create_builtin_fn(g, BuiltinFnIdIntType, "intType", 2);
     create_builtin_fn(g, BuiltinFnIdUnreachable, "unreachable", 0);
     create_builtin_fn(g, BuiltinFnIdSetFnTest, "setFnTest", 1);