add detection rule for FFmpeg/Lego1 (ELF)

Introduces new ELF signatures, those were mostly ported from the PE variant

Author: BJNFNE

db/ELF/FFmpeg.4.sg

@@ -0,0 +1,13 @@
+// Detect It Easy: detection rule file
+// Author: BJNFNE <[email protected]>
+
+// https://ffmpeg.com/
+meta("library", "FFmpeg");
+
+function detect() {
+    if (ELF.isLibraryPresent("libffmpeg.so")) {
+        bDetected = true;
+    }
+
+    return result();
+}

db/ELF/Lego1.4.sg

@@ -0,0 +1,13 @@
+// Detect It Easy: detection rule file
+// Author: BJNFNE <[email protected]>
+
+// https://github.com/isledecomp/isle-portable
+meta("library", "Lego1");
+
+function detect() {
+    if (ELF.isLibraryPresent("liblego1.so")) {
+        bDetected = true;
+    }
+
+    return result();
+}