Add targets of symlinks to genrule's sources

A change is being made to sbox so that symlinks aren't resolved
before being copied into the sandbox. This requires that the targets
of the symlinks are also added to the sandbox.

Bug: 307824623
Test: m libc_musl_sysroot_libc++_headers with aosp/2850015
Change-Id: Idc46c38a2c92826b52d82add8221c69c2f1394fe

Android.bp

@@ -294,8 +294,10 @@ genrule {
     name: "libc_musl_sysroot_libc++_headers",
     visibility: ["//external/musl"],
     srcs: [
+        "LICENSE.TXT",
         "NOTICE",
         "include/**/*",
+        ":libcxxabi_headers",
     ],
     out: ["libc_musl_sysroot_libc++_headers.zip"],
     tools: [