Correctly check for HAVE_STAT_BIRTHTIME in configure.ac checks for Sy…

…stem.Native (#16999)

The check was done incorrectly, the include files need to be separated by newlines otherwise we would get a false negative result.

config.log contained this:

```
conftest.c:279:23: warning: extra tokens at end of #include directive [-Wextra-tokens]
#include <sys/types.h>, #include <sys/stat.h>
                      ^
                      //
```

This means that when doing File.GetCreationTime() we'd fall back to returning the last modified time.

It regressed when we switched to System.IO.File to the CoreFX implementation i.e. System.Native in 8f5cef9.

Fixes #16974

configure.ac

@@ -3400,13 +3400,29 @@ if test x$host_win32 = xno; then
 	AC_CHECK_DECL(ICANON,            [AC_DEFINE(HAVE_ICANON, 1, [ICANON])], [], [[#include <termios.h>]])
 	AC_CHECK_DECL(TCSANOW,           [AC_DEFINE(HAVE_TCSANOW, 1, [TCSANOW])], [], [[#include <termios.h>]])
 
-	AC_CHECK_MEMBER(struct stat.st_birthtimespec, [AC_DEFINE(HAVE_STAT_BIRTHTIME, 1, [struct stat.st_birthtime])], [], [[#include <sys/types.h>], [#include <sys/stat.h>]])
-	AC_CHECK_MEMBER(struct stat.st_atimespec,     [AC_DEFINE(HAVE_STAT_TIMESPEC, 1, [struct stat.st_atimespec])], [], [[#include <sys/types.h>], [#include <sys/stat.h>]])
-	AC_CHECK_MEMBER(struct stat.st_atim,          [AC_DEFINE(HAVE_STAT_TIM, 1, [struct stat.st_atim])], [], [[#include <sys/types.h>], [#include <sys/stat.h>]])
-	AC_CHECK_MEMBER(struct stat.st_atimensec,     [AC_DEFINE(HAVE_STAT_NSEC, 1, [struct stat.st_atimensec])], [], [[#include <sys/types.h>], [#include <sys/stat.h>]])
-	AC_CHECK_MEMBER(struct dirent.d_namlen,       [AC_DEFINE(HAVE_DIRENT_NAME_LEN, 1, [struct dirent.d_namlen])], [], [[#include <dirent.h>]])
-	AC_CHECK_MEMBER(struct statfs.f_fstypename,   [AC_DEFINE(HAVE_STATFS_FSTYPENAME, 1, [struct statfs.f_fstypename])], [], [[#include <sys/mount.h>]])
-	AC_CHECK_MEMBER(struct statvfs.f_fstypename,  [AC_DEFINE(HAVE_STATVFS_FSTYPENAME, 1, [struct statvfs.f_fstypename])], [], [[#include <sys/mount.h>]])
+	AC_CHECK_MEMBER(struct stat.st_birthtimespec,
+		[AC_DEFINE(HAVE_STAT_BIRTHTIME, 1, [struct stat.st_birthtimespec])],
+		[],
+		[#include <sys/types.h>
+		#include <sys/stat.h>])
+	AC_CHECK_MEMBER(struct stat.st_atimespec,
+		[AC_DEFINE(HAVE_STAT_TIMESPEC, 1, [struct stat.st_atimespec])],
+		[],
+		[#include <sys/types.h>
+		#include <sys/stat.h>])
+	AC_CHECK_MEMBER(struct stat.st_atim,
+		[AC_DEFINE(HAVE_STAT_TIM, 1, [struct stat.st_atim])],
+		[],
+		[#include <sys/types.h>
+		#include <sys/stat.h>])
+	AC_CHECK_MEMBER(struct stat.st_atimensec,
+		[AC_DEFINE(HAVE_STAT_NSEC, 1, [struct stat.st_atimensec])],
+		[],
+		[#include <sys/types.h>
+		#include <sys/stat.h>])
+	AC_CHECK_MEMBER(struct dirent.d_namlen,       [AC_DEFINE(HAVE_DIRENT_NAME_LEN, 1, [struct dirent.d_namlen])], [], [#include <dirent.h>])
+	AC_CHECK_MEMBER(struct statfs.f_fstypename,   [AC_DEFINE(HAVE_STATFS_FSTYPENAME, 1, [struct statfs.f_fstypename])], [], [#include <sys/mount.h>])
+	AC_CHECK_MEMBER(struct statvfs.f_fstypename,  [AC_DEFINE(HAVE_STATVFS_FSTYPENAME, 1, [struct statvfs.f_fstypename])], [], [#include <sys/mount.h>])
 
 	AC_MSG_CHECKING(for struct statfs)
 	AC_TRY_COMPILE([