[PATCH] tools/nolibc: make time_t robust if __kernel_old_time_t is missing in host headers

[Zhouyi Zhou <zhouzhouyi@gmail.com>]

Commit 
d5094bcb5bfd ("tools/nolibc: define time_t in terms of __kernel_old_time_t")
made nolibc use the kernel's time type so that `time_t` matches
`timespec::tv_sec` on all ABIs (notably x32).    

Some distributions (e.g. Ubuntu 20.04 on ppc64le with older
exported headers under /usr/include) do not expose
`__kernel_old_time_t`, causing nolibc builds that rely on host
headers to fail (I discovered this when doing RCU torture test in
PPC VM of Open Source Lab of Oregon State University).
        
Keep the new behavior, but add a small compatibility shim:
if `__kernel_old_time_t` is not available, fall back to
 `signed long`

This preserves the intent of d5094bcb5bfd while letting nolibc
build on systems with older exported headers.

Fixes: d5094bcb5bfd ("tools/nolibc: define time_t in terms of __kernel_old_time_t")
Signed-off-by: Zhouyi Zhou <zhouzhouyi@gmail.com>    
---
 tools/include/nolibc/std.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/include/nolibc/std.h b/tools/include/nolibc/std.h
index ba950f0e7338..ea225a0b16e9 100644
--- a/tools/include/nolibc/std.h
+++ b/tools/include/nolibc/std.h
@@ -29,6 +29,10 @@ typedef unsigned long       nlink_t;
 typedef   signed long         off_t;
 typedef   signed long     blksize_t;
 typedef   signed long      blkcnt_t;
+#ifndef __kernel_old_time_t
+typedef   signed long        time_t;
+#else
 typedef __kernel_old_time_t  time_t;
+#endif
 
 #endif /* _NOLIBC_STD_H */
-- 
2.25.1