[pstl] Default to the serial backend when unspecified
This is a stopgap measure to make it easier to integrate the PSTL into
libc++. In the future, we should have a system similar to what libc++
does, where we specify settings at configuration time and generate a
__config_site header that is part of the PSTL.
llvm-svn: 363958
GitOrigin-RevId: 04c5bc989a31b81bd7dda1f3e53de2930c8c7ec0
diff --git a/include/pstl/internal/pstl_config.h b/include/pstl/internal/pstl_config.h
index 72f31c3..3c2b146 100644
--- a/include/pstl/internal/pstl_config.h
+++ b/include/pstl/internal/pstl_config.h
@@ -17,7 +17,9 @@
#define _PSTL_VERSION_PATCH (_PSTL_VERSION % 10)
#if !defined(_PSTL_PAR_BACKEND_SERIAL) && !defined(_PSTL_PAR_BACKEND_TBB)
-# error "The parallel backend is neither serial nor TBB"
+// TODO: In the future, we need to handle this setting using a configure-time
+// option and something like a __config_site header.
+# define _PSTL_PAR_BACKEND_SERIAL
#endif
// Check the user-defined macro for warnings
