Rollup merge of #97840 - durin42:llvm-15-apint, r=nikic

RustWrapper: adapt to APInt API changes in LLVM 15

In https://reviews.llvm.org/D125556 upstream changed sext() and zext()
to allow some no-op cases, which previously required use of the *OrSelf()
methods, which I assume is what was going on here. The *OrSelf() methods
got removed in https://reviews.llvm.org/D125559 after two weeks of
deprecation because they came with some bonus (probably-undesired)
behavior. Since the behavior of sext() and zext() changed slightly, I
kept the old *OrSelf() calls in LLVM 14 and earlier, and only use the
new version in LLVM 15.

r? `@nikic`

compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp

@@ -1542,11 +1542,19 @@ extern "C" bool LLVMRustConstInt128Get(LLVMValueRef CV, bool sext, uint64_t *hig
     auto C = unwrap<llvm::ConstantInt>(CV);
     if (C->getBitWidth() > 128) { return false; }
     APInt AP;
+#if LLVM_VERSION_GE(15, 0)
+    if (sext) {
+        AP = C->getValue().sext(128);
+    } else {
+        AP = C->getValue().zext(128);
+    }
+#else
     if (sext) {
         AP = C->getValue().sextOrSelf(128);
     } else {
         AP = C->getValue().zextOrSelf(128);
     }
+#endif
     *low = AP.getLoBits(64).getZExtValue();
     *high = AP.getHiBits(64).getZExtValue();
     return true;