[libcxx] Do not include the C math.h header before __config
Summary:
Certain C libraries require configuration macros defined in __config
to provide the correct functionality for libc++. This patch ensures
that the C header math.h is always included after the __config
header. It also adds a Windows-specific #if guard for the case when
the C math.h file is included the second time, as suggested by
Marshall in https://reviews.llvm.org/rL323490.
Fixes PR36382.
Reviewers: mclow.lists, EricWF
Reviewed By: mclow.lists
Subscribers: cfe-commits, pcc, christof, rogfer01
Differential Revision: https://reviews.llvm.org/D43579
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@325760 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/math.h b/include/math.h
index 1476772..cd055ca 100644
--- a/include/math.h
+++ b/include/math.h
@@ -8,16 +8,6 @@
//
//===----------------------------------------------------------------------===//
-// This include lives outside the header guard in order to support an MSVC
-// extension which allows users to do:
-//
-// #define _USE_MATH_DEFINES
-// #include <math.h>
-//
-// and receive the definitions of mathematical constants, even if <math.h>
-// has previously been included.
-#include_next <math.h>
-
#ifndef _LIBCPP_MATH_H
#define _LIBCPP_MATH_H
@@ -308,6 +298,8 @@
#pragma GCC system_header
#endif
+#include_next <math.h>
+
#ifdef __cplusplus
// We support including .h headers inside 'extern "C"' contexts, so switch
@@ -1494,4 +1486,18 @@
#endif // __cplusplus
+#else // _LIBCPP_MATH_H
+
+// This include lives outside the header guard in order to support an MSVC
+// extension which allows users to do:
+//
+// #define _USE_MATH_DEFINES
+// #include <math.h>
+//
+// and receive the definitions of mathematical constants, even if <math.h>
+// has previously been included.
+#if defined(_LIBCPP_MSVCRT) && defined(_USE_MATH_DEFINES)
+#include_next <math.h>
+#endif
+
#endif // _LIBCPP_MATH_H
