package/gdb: disable gdb for or1k builds with musl libc

The or1k musl port is incomplete, elf_gregset_t definition is missing
(user.h is empty) [1]. It fail to build gdbserver and the full gdb.

[1] https://git.musl-libc.org/cgit/musl/tree/arch/or1k/bits/user.h?h=v1.2.3

Fixes:
https://gitlab.com/buildroot.org/toolchains-builder/-/jobs/4202276569

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Cc: Stafford Horne <shorne@gmail.com>
[yann.morin.1998@free.fr: simplify condition, add comment]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/gdb/Config.in

@@ -4,6 +4,10 @@ config BR2_PACKAGE_GDB_ARCH_SUPPORTS
 	depends on !((BR2_arm || BR2_armeb) && BR2_BINFMT_FLAT)
 	depends on !BR2_microblaze
 
+comment "gdb needs a glibc or uclibc toolchain"
+	depends on BR2_or1k
+	depends on BR2_TOOLCHAIN_USES_MUSL
+
 comment "gdb/gdbserver needs a toolchain w/ threads, threads debug"
 	depends on BR2_PACKAGE_GDB_ARCH_SUPPORTS
 	depends on !BR2_TOOLCHAIN_HAS_THREADS || !BR2_TOOLCHAIN_HAS_THREADS_DEBUG
@@ -17,6 +21,9 @@ config BR2_PACKAGE_GDB
 	depends on BR2_PACKAGE_GDB_ARCH_SUPPORTS
 	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_4_8
 	depends on BR2_INSTALL_LIBSTDCPP
+	# The or1k musl port is incomplete, elf_gregset_t definition is missing:
+	# https://git.musl-libc.org/cgit/musl/tree/arch/or1k/bits/user.h?h=v1.2.3
+	depends on !BR2_or1k || !BR2_TOOLCHAIN_USES_MUSL
 	select BR2_PACKAGE_ZLIB
 	# When the external toolchain gdbserver is copied to the
 	# target, we don't allow building a separate gdbserver. The