feat(musl-fts): add steps-guix musl-fts-1.2.7 build step and wire it into manifest

steps-guix/musl-fts-1.2.7/pass1.sh

@@ -0,0 +1,34 @@
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+# Build musl-fts for the kernel toolchain sysroot.
+: "${KERNEL_SYSROOT:=/kernel-toolchain}"
+
+src_prepare() {
+    default
+    autoreconf -fi
+}
+
+src_configure() {
+    mkdir build
+    cd build
+
+    CC=gcc \
+    AR=ar \
+    RANLIB=ranlib \
+    ../configure \
+        --prefix="${KERNEL_SYSROOT}" \
+        --libdir="${KERNEL_SYSROOT}/lib" \
+        --includedir="${KERNEL_SYSROOT}/include"
+}
+
+src_compile() {
+    default_src_compile
+}
+
+src_install() {
+    make "${MAKEJOBS}" install \
+        DESTDIR="${DESTDIR}" \
+        prefix="${KERNEL_SYSROOT}" \
+        libdir="${KERNEL_SYSROOT}/lib" \
+        includedir="${KERNEL_SYSROOT}/include"
+}

steps-guix/musl-fts-1.2.7/sources

@@ -0,0 +1 @@
+f https://sources.cdn.openwrt.org/musl-fts-1.2.7.tar.xz 29c62a80e01f22bb4c998f13ef8bd33b5d7ada51231f0ef267f0f67f1be58ff5