Revert backtrace ban and start printing backtraces from the runtime again (#9528)

* Revert "[strip -ST] Disable runtime stack trace dumping on Darwin when asserts are disabled."
This reverts commit 6bc28ff1c9.
* Bring back important fixes from the revert of 6bc28ff1c9.
* Change swift::swift_reportError to only print the backtrace in assert builds (swift::warning prints backtrace always).

stdlib/public/runtime/ImageInspectionELF.cpp

@@ -27,10 +27,6 @@
 #include <link.h>
 #include <string.h>
 
-#ifndef SWIFT_RUNTIME_DLADDR_ALLOW
-#error "SWIFT_RUNTIME_DLADDR_ALLOW must be defined!"
-#endif
-
 using namespace swift;
 
 /// The symbol name in the image that identifies the beginning of the
@@ -162,7 +158,6 @@ void swift_addNewDSOImage(const void *addr) {
 }
 
 int swift::lookupSymbol(const void *address, SymbolInfo *info) {
-#if SWIFT_RUNTIME_DLADDR_ALLOW
   Dl_info dlinfo;
   if (dladdr(address, &dlinfo) == 0) {
     return 0;
@@ -173,9 +168,6 @@ int swift::lookupSymbol(const void *address, SymbolInfo *info) {
   info->symbolName = dlinfo.dli_sname;
   info->symbolAddress = dlinfo.dli_saddr;
   return 1;
-#else
-  return 0;
-#endif
 }
 
 #endif // defined(__ELF__) || defined(__ANDROID__)