toolchain/toolchain-buildroot, package/glibc: sync glibc dependency comments

In commit fd839aeb7f40596e60bc53a96b7a65892924cc26 ("package/glibc:
introduce and use BR2_PACKAGE_GLIBC_ARCH_SUPPORTS and
BR2_PACKAGE_GLIBC_SUPPORTS") we moved the Config.in logic about glibc
dependencies from toolchain/toolchain-buildroot/Config.in into
package/glibc/Config.in.

Unfortunately, it is not possible to move the Config.in comments that
tell the user, within the choice..endchoice for the C library why
glibc is not currently selectable, so we had to keep them in
toolchain/toolchain-buildroot/Config.in.

Turns out that the comments were out of sync with the dependencies,
and two comments were missing. This commit adds the missing ones, and
adds a comment in package/glibc/Config.in explaining that we need to
be careful about updating toolchain/toolchain-buildroot/Config.in as
well.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/glibc/Config.in

@@ -30,6 +30,9 @@ config BR2_PACKAGE_GLIBC_SUPPORTS
 	bool
 	default y if BR2_PACKAGE_GLIBC_ARCH_SUPPORTS
 	depends on !BR2_STATIC_LIBS
+	# Make sure to keep these dependencies in sync with the
+	# Config.in comments in
+	# toolchain/toolchain-buildroot/Config.in
 	depends on BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_2
 	depends on BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_10 || !BR2_powerpc64le
 	depends on BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_5 || !BR2_MIPS_NAN_2008

toolchain/toolchain-buildroot/Config.in

@@ -64,6 +64,14 @@ comment "glibc on MIPS w/ NAN2008 needs a toolchain w/ headers >= 4.5"
 	depends on BR2_MIPS_NAN_2008
 	depends on !BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_5
 
+comment "glibc on RISC-V 64-bit needs a toolchain w/ headers >= 5.0"
+	depends on BR2_RISCV_64
+	depends on !BR2_TOOLCHAIN_HEADERS_AT_LEAST_5_0
+
+comment "glibc on ARC needs a toolchain w/ headers >= 5.1"
+	depends on BR2_arc
+	depends on !BR2_TOOLCHAIN_HEADERS_AT_LEAST_5_1
+
 config BR2_TOOLCHAIN_BUILDROOT_MUSL
 	bool "musl"
 	depends on BR2_PACKAGE_MUSL_SUPPORTS