feat(elb): c_source manifest directive + macOS OpenSSL path detection

Add `c_source "path"` in manifest.el build block — lets packages link
extra C files (platform stubs, native glue) without touching elb source.

On macOS, homebrew OpenSSL isn't on the default linker path. Detect it
via `brew --prefix` and inject -L/-I flags; no-op on Linux.

Rebuild elb binary; remove elc-new binary (elc is now canonical).

lang/elb.el

@@ -77,6 +77,33 @@ fn parse_manifest_entry(src: String) -> String {
     return ""
 }
 
+// parse_manifest_c_sources - collect all `c_source "path"` lines from the
+// build block.  Returns a flat list of path strings.
+fn parse_manifest_c_sources(src: String) -> [String] {
+    let result: [String] = native_list_empty()
+    let lines: [String] = str_split(src, "\n")
+    let n: Int = native_list_len(lines)
+    let i = 0
+    while i < n {
+        let line: String = native_list_get(lines, i)
+        let t: String = str_trim(line)
+        if str_starts_with(t, "c_source ") {
+            let after: String = str_slice(t, 9, str_len(t))
+            let trimmed: String = str_trim(after)
+            if str_starts_with(trimmed, "\"") {
+                let inner: String = str_slice(trimmed, 1, str_len(trimmed))
+                let q: Int = str_index_of(inner, "\"")
+                if q >= 0 {
+                    let path: String = str_slice(inner, 0, q)
+                    let result = native_list_append(result, path)
+                }
+            }
+        }
+        let i = i + 1
+    }
+    return result
+}
+
 fn parse_manifest_name(src: String) -> String {
     let lines: [String] = str_split(src, "\n")
     let n: Int = native_list_len(lines)
@@ -274,7 +301,11 @@ fn link_binary(c_files: [String], out_bin: String, runtime_path: String, out_dir
     // Detect clang vs gcc: -fbracket-depth is clang-only; silently ignored
     // if unsupported but gcc rejects it with an error.
     let bracket_flag: String = "$(cc --version 2>&1 | grep -q clang && printf -- '-fbracket-depth=1024' || true)"
-    let parts = native_list_append(parts, "cc -O2 " + bracket_flag + " -I " + dirname_of(runtime_path) + " -I " + out_dir)
+    // On macOS, OpenSSL is not on the default linker path. Detect homebrew
+    // prefix and add it if present (no-op on Linux where libssl is in /usr/lib).
+    let ossl_lib_flag: String = "$(brew --prefix openssl 2>/dev/null | xargs -I{} printf -- '-L{}/lib' 2>/dev/null || true)"
+    let ossl_inc_flag: String = "$(brew --prefix openssl 2>/dev/null | xargs -I{} printf -- '-I{}/include' 2>/dev/null || true)"
+    let parts = native_list_append(parts, "cc -O2 " + bracket_flag + " " + ossl_inc_flag + " -I " + dirname_of(runtime_path) + " -I " + out_dir)
     let i = 0
     while i < n {
         let f: String = native_list_get(c_files, i)
@@ -282,7 +313,7 @@ fn link_binary(c_files: [String], out_bin: String, runtime_path: String, out_dir
         let i = i + 1
     }
     let parts = native_list_append(parts, runtime_path)
-    let parts = native_list_append(parts, "-lcurl -lssl -lcrypto -lpthread -lm")
+    let parts = native_list_append(parts, ossl_lib_flag + " -lcurl -lssl -lcrypto -lpthread -lm")
     let parts = native_list_append(parts, "-o " + out_bin)
     let cmd: String = str_join(parts, " ")
     println("  link     " + out_bin)
@@ -315,6 +346,7 @@ fn main() -> Void {
 
     let pkg_name: String = parse_manifest_name(manifest_src)
     let entry: String    = parse_manifest_entry(manifest_src)
+    let extra_c: [String] = parse_manifest_c_sources(manifest_src)
     if str_eq(entry, "") {
         println("elb: manifest.el has no 'entry' declaration")
         exit(1)
@@ -393,6 +425,15 @@ fn main() -> Void {
         exit(1)
     }
 
+    // Append any extra C sources declared in the manifest (e.g. platform stubs)
+    let ei = 0
+    let en: Int = native_list_len(extra_c)
+    while ei < en {
+        let ec: String = native_list_get(extra_c, ei)
+        let c_files = native_list_append(c_files, ec)
+        let ei = ei + 1
+    }
+
     // Link
     let out_bin: String = out_dir + "/" + pkg_name
     let linked: Bool = link_binary(c_files, out_bin, runtime_path, out_dir, dry_run)