Revert "[APInt] Enable APInt ctor assertion by default (#112670)"

This reverts commit ba1ee2b.

Causes some buildbot failures on aarch64.

Author: nikic

llvm/include/llvm/ADT/APInt.h

@@ -109,7 +109,7 @@ class [[nodiscard]] APInt {
   /// \param implicitTrunc allow implicit truncation of non-zero/sign bits of
   ///                      val beyond the range of numBits
   APInt(unsigned numBits, uint64_t val, bool isSigned = false,
-        bool implicitTrunc = false)
+        bool implicitTrunc = true)
       : BitWidth(numBits) {
     if (!implicitTrunc) {
       if (isSigned) {