Fix uninitialized IRGenOptions field

#42094 added a new `IRGenOptions::CompactAbsoluteFunctionPointer` field, but did not initialize it. We subsequently started seeing flaky test failures in LLDB tests that tried to resolve relocations in metadata, so we think this may have resulted in the option sometimes being set to `true` in the REPL.

Author: beccadax

include/swift/AST/IRGenOptions.h

@@ -446,7 +446,8 @@ class IRGenOptions {
         EnableReflectionNames(true), EnableAnonymousContextMangledNames(false),
         ForcePublicLinkage(false), LazyInitializeClassMetadata(false),
         LazyInitializeProtocolConformances(false),
-        IndirectAsyncFunctionPointer(false), DisableLegacyTypeInfo(false),
+        IndirectAsyncFunctionPointer(false),
+        CompactAbsoluteFunctionPointer(false), DisableLegacyTypeInfo(false),
         PrespecializeGenericMetadata(false), UseIncrementalLLVMCodeGen(true),
         UseTypeLayoutValueHandling(true), ForceStructTypeLayouts(false),
         GenerateProfile(false), EnableDynamicReplacementChaining(false),