The problem is basically that sys/ucontext.h is defining R0..R15
which happens to conflict with some packages like Firefox when
trying to build on SH.
The very same problem existed on arm back then [1] and it was fixed by
renaming R0..R15 to REG_R0..REG_R15. This patch imploy a similar
strategy for SH.
Checked on sh4-linux-gnu with run-built-tests=no and I also got reports
that it fixes Firefox build on Debian sh4.
* sysdeps/unix/sysv/linux/sh/sh3/ucontext_i.sym: Use new REG_R*
constants instead of the old R* ones.
* sysdeps/unix/sysv/linux/sh/sh4/ucontext_i.sym: Likewise.
* sysdeps/unix/sysv/linux/sh/sys/ucontext.h (NGPREG): Rename...
(NGREG): ... to this, to fit in with other architectures.
(gpregset_t): Use new NGREG macro.
[__USE_GNU]: Remove condition; all architectures other than tile
are unconditional.
(R*): Rename to REG_R*.
