package/glibc: glibc on or1k needs a toolchain w/ headers >= 5.4

Commit [1] enabled glibc on or1k since it's now supported but it
requires a toolchain with linux-headers >= 5.4.

From [2]:
"Here we define the minumum linux kernel version at 5.4.0, as that is the
long term support version where 32-bit architectures start to support
64-bit time API's.  The OpenRISC kernel had some bugs up until version 5.8
which caused issues with glibc fork/clone, they have been backported to
5.4 but not previous versions."

Fixes:

  checking installed Linux kernel header files... 3.2.0 or later
  checking for kernel header at least 5.4.0... too old!
  configure: error: *** The available kernel headers are older than the requested

https://gitlab.com/buildroot.org/toolchains-builder/-/jobs/2875256686

[1] 68d0aede
[2] https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=0c3c62ca7d9ff3bdacdd13e636bc858101e3e288



Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Arnout Vandecappelle <arnout@mind.be>