[flang] Don't redefine pid_t on MinGW-w64. (#130288)

GitOrigin-RevId: cf5aa559a8b69bc39ba134148ace4172fd6de0a8
diff --git a/include/flang/Optimizer/Builder/Runtime/RTBuilder.h b/include/flang/Optimizer/Builder/Runtime/RTBuilder.h
index 5158aba..722e919 100644
--- a/include/flang/Optimizer/Builder/Runtime/RTBuilder.h
+++ b/include/flang/Optimizer/Builder/Runtime/RTBuilder.h
@@ -30,7 +30,7 @@
 #include <cstdint>
 #include <functional>
 
-#ifdef _WIN32
+#ifdef _MSC_VER
 // On Windows* OS GetCurrentProcessId returns DWORD aka uint32_t
 typedef std::uint32_t pid_t;
 #endif
diff --git a/include/flang/Runtime/command.h b/include/flang/Runtime/command.h
index 7ab3f64..3add66d 100644
--- a/include/flang/Runtime/command.h
+++ b/include/flang/Runtime/command.h
@@ -12,7 +12,7 @@
 #include "flang/Runtime/entry-names.h"
 #include <cstdint>
 
-#ifdef _WIN32
+#ifdef _MSC_VER
 // On Windows* OS GetCurrentProcessId returns DWORD aka uint32_t
 typedef std::uint32_t pid_t;
 #else