audit: add an explanation of musl disable

Based on commit c17af71d2c2 (package/audit: not available for musl) add a
comment that explains why audit is disabled for musl.

Cc: Yann E. MORIN <yann.morin.1998@free.fr>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/audit/Config.in

@@ -10,7 +10,7 @@ config BR2_PACKAGE_AUDIT
 	depends on BR2_PACKAGE_AUDIT_ARCH_SUPPORTS
 	depends on BR2_TOOLCHAIN_HAS_THREADS
 	depends on !BR2_STATIC_LIBS
-	depends on !BR2_TOOLCHAIN_USES_MUSL
+	depends on !BR2_TOOLCHAIN_USES_MUSL # strndupa()
 	help
 	  The audit package contains the user space utilities for
 	  storing and searching the audit records generated by