fix build issue by making _FortranAGetMainThreadId() a runtime routine

Author: gregrodgers

flang-rt/lib/runtime/main.cpp

@@ -13,8 +13,6 @@
 #include <cstdio>
 #include <cstdlib>
 #include <thread>
-std::thread::id main_thread_id = std::this_thread::get_id();
-extern "C" std::thread::id get_main_thread_id() { return main_thread_id; }
 
 static void ConfigureFloatingPoint() {
 #ifdef feclearexcept // a macro in some environments; omit std::
@@ -29,7 +27,10 @@ static void ConfigureFloatingPoint() {
 #endif
 }
 
+std::thread::id _main_thread_id = std::this_thread::get_id();
 extern "C" {
+std::thread::id RTNAME(GetMainThreadId)() { return _main_thread_id; }
+
 void RTNAME(ProgramStart)(int argc, const char *argv[], const char *envp[],
     const EnvironmentDefaultList *envDefaults) {
   std::atexit(Fortran::runtime::NotifyOtherImagesOfNormalEnd);

flang-rt/lib/runtime/stop.cpp

@@ -13,11 +13,11 @@
 #include "flang-rt/runtime/file.h"
 #include "flang-rt/runtime/io-error.h"
 #include "flang-rt/runtime/terminator.h"
+#include "flang/Runtime/main.h"
 #include <cfenv>
 #include <cstdio>
 #include <cstdlib>
 #include <thread>
-std::thread::id get_main_thread_id();
 
 #ifdef HAVE_BACKTRACE
 #include BACKTRACE_HEADER
@@ -81,7 +81,7 @@ static void CloseAllExternalUnits(const char *why) {
     std::fputc('\n', stderr);
     DescribeIEEESignaledExceptions();
   }
-  if (get_main_thread_id() != std::this_thread::get_id())
+  if (RTNAME(GetMainThreadId)() != std::this_thread::get_id())
     std::abort();
   std::exit(code);
 }
@@ -98,7 +98,7 @@ static void CloseAllExternalUnits(const char *why) {
     }
     DescribeIEEESignaledExceptions();
   }
-  if (get_main_thread_id() != std::this_thread::get_id())
+  if (RTNAME(GetMainThreadId)() != std::this_thread::get_id())
     std::abort();
   if (isErrorStop) {
     std::exit(EXIT_FAILURE);

flang/include/flang/Runtime/main.h

@@ -11,10 +11,12 @@
 
 #include "flang/Runtime/c-or-cpp.h"
 #include "flang/Runtime/entry-names.h"
+#include <thread>
 
 struct EnvironmentDefaultList;
 
 FORTRAN_EXTERN_C_BEGIN
+std::thread::id RTNAME(GetMainThreadId)();
 void RTNAME(ProgramStart)(
     int, const char *[], const char *[], const struct EnvironmentDefaultList *);
 void RTNAME(ByteswapOption)(void); // -byteswapio