dev-libs/npth: Sync with Gentoo

It's from Gentoo commit 35606cd7f9fb29a4c83847cfc00ef364f85287a8.

sdk_container/src/third_party/portage-stable/dev-libs/npth/files/npth-1.7-musl.patch

@@ -0,0 +1,16 @@
+https://bugs.gentoo.org/925443
+https://dev.gnupg.org/T5664
+--- a/configure.ac
++++ b/configure.ac
+@@ -381,7 +381,10 @@ fi
+ AC_SUBST(INSERT_NO_RWLOCK)
+ 
+ case "${host}" in
+-    *-*-linux*|*-*-gnu*)
++    *-*-linux-musl*)
++        INSERT_EXPOSE_RWLOCK_API="1"
++        ;;
++    *-*-linux-gnu*|*-*-gnu*)
+         INSERT_EXPOSE_RWLOCK_API="defined(__USE_UNIX98) || defined(__USE_XOPEN2K)"
+         ;;
+     *)

sdk_container/src/third_party/portage-stable/dev-libs/npth/npth-1.7-r1.ebuild

@@ -15,6 +15,10 @@ KEYWORDS="~alpha ~amd64 ~arm ~arm64 ~hppa ~ia64 ~loong ~m68k ~mips ~ppc ~ppc64 ~
 IUSE="test"
 RESTRICT="!test? ( test )"
 
+PATCHES=(
+	"${FILESDIR}"/${P}-musl.patch
+)
+
 src_prepare() {
 	default
 	eautoreconf