internal/rosa/package: migrate musl

This removes some legacy cruft, causing 2 rebuilds per stage.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/package/musl/ldso-rosa.patch

@@ -0,0 +1,13 @@
+diff --git a/ldso/dynlink.c b/ldso/dynlink.c
+index 715948f4..c2fece68 100644
+--- a/ldso/dynlink.c
++++ b/ldso/dynlink.c
+@@ -1157,7 +1157,7 @@ static struct dso *load_library(const char *name, struct dso *needed_by)
+ 					sys_path = "";
+ 				}
+ 			}
+-			if (!sys_path) sys_path = "/lib:/usr/local/lib:/usr/lib";
++			if (!sys_path) sys_path = "/system/lib:/system/lib/" LDSO_ARCH "-rosa-linux-musl:/lib:/usr/local/lib:/usr/lib";
+ 			fd = path_open(name, sys_path, buf, sizeof buf);
+ 		}
+ 		pathname = buf;

internal/rosa/package/musl/package.az

@@ -0,0 +1,70 @@
+package musl-source {
+	description = "an implementation of the C standard library - source code";
+
+	version* = "1.2.6";
+	output = remoteTar {
+		url = "https://musl.libc.org/releases/musl-"+version+".tar.gz";
+		checksum = "WtWb_OV_XxLDAB5NerOL9loLlHVadV00MmGk65PPBU1evaolagoMHfvpZp_vxEzS";
+		compress = gzip;
+	};
+}
+
+package musl-headers {
+	description = "system installation of musl headers";
+
+	source = musl-source;
+
+	// expected to be writable in copies
+	chmod = true;
+
+	env = [
+		"LDFLAGS=" + earlyLDFLAGS,
+	];
+
+	exec = make {
+		omitDefaults = true;
+		skipCheck = true;
+
+		make = [
+			"DESTDIR=/work",
+			"install-headers",
+		];
+
+		install = "# headers installed during make";
+	};
+
+	inputs = [ coreutils ];
+}
+
+package musl {
+	description = "an implementation of the C standard library";
+	website = "https://musl.libc.org";
+	anitya = 11688;
+
+	source = musl-source;
+	patches = [ "ldso-rosa.patch" ];
+
+	// expected to be writable in copies
+	chmod = true;
+
+	env = [
+		"LDFLAGS=" + earlyLDFLAGS,
+	];
+
+	exec = make {
+		omitDefaults = true;
+		skipCheck = true;
+
+		postInstall = `
+mkdir -p /work/system/bin
+COMPAT_LINKER_NAME="ld-musl-` + linuxArch + `.so.1"
+ln -vs ../lib/libc.so /work/system/bin/linker
+ln -vs ../lib/libc.so /work/system/bin/ldd
+ln -vs libc.so "/work/system/lib/${COMPAT_LINKER_NAME}"
+rm -v "/work/lib/${COMPAT_LINKER_NAME}"
+rmdir -v /work/lib
+`;
+	};
+
+	inputs = [ coreutils ];
+}