Consider MIT WITH Musl-Exception as a single permissive license

```
In addition, permission is hereby granted for all public header files
(include/* and arch/*/bits/*) and crt files intended to be linked into
applications (crt/*, ldso/dlstart.c, and arch/*/crt_arch.h) to omit
the copyright notice and permission notice otherwise required by the
license, and to use these files without any requirement of
attribution. These files include substantial contributions from:
```

It waives up the copyright restriction otherwise imposed by MIT license.
There is no need to forbid this license.

build/conf/license.conf

@@ -188,7 +188,6 @@ LICENSES_FORBIDDEN= \
     AGPL-3.0-only \
     AGPL-3.0-or-later \
     Artistic-1.0 \
-    Musl-Exception \
     confluent-community-1.0 \
     ${LICENSES_UNATTRIBUTED}
 
@@ -328,6 +327,7 @@ LICENSES_REQUIRE_CITATION= \
     Mit-Old-Style \
     MIT-open-group \
     Mit-Veillard-Variant \
+    MIT WITH Musl-Exception \
     Mozilla-GC \
     MPL-1.0 \
     MPL-1.1 \
@@ -386,7 +386,6 @@ LICENSES_REQUIRE_CITATION= \
     zlib-acknowledgement \
     ZPL-2.1 \
     ${CUSTOM_LICENSE_LINUX_SYSCALL_NOTE} \
-    ${CUSTOM_LICENSE_MUSL_EXCEPTION} \
     ${LICENSES_PATCHES_FORBIDDEN} \
 
 LICENSES_REQUIRE_CITATION_DYNAMIC= \
@@ -400,8 +399,6 @@ LICENSES_REQUIRE_CITATION_DYNAMIC= \
 
 # Permissive if the code is used to declare and invoke syscalls
 CUSTOM_LICENSE_LINUX_SYSCALL_NOTE=Linux-syscall-note-in-syscall-glue
-# Permissive only in musllib
-CUSTOM_LICENSE_MUSL_EXCEPTION=Musl-Exception-in-Musllib
 
 LICENSES_SERVICE= \
     Service-Default-License \