liblz4: fix build & installation steps

* Run only `make install` to avoid compiling libs & tools 2 times.

* Always use `ln -sf` when creating symlinks.

packages/liblz4/Makefile.inc.patch

@@ -0,0 +1,12 @@
+diff -uNr lz4-1.9.2/Makefile.inc lz4-1.9.2.mod/Makefile.inc
+--- lz4-1.9.2/Makefile.inc	2019-08-15 14:59:59.000000000 +0300
++++ lz4-1.9.2.mod/Makefile.inc	2019-09-09 03:40:49.761918035 +0300
+@@ -70,7 +70,7 @@
+ LN_S  = cp -p
+ LN_SF = cp -p
+     else
+-LN_S   = ln -s
++LN_S   = ln -sf
+ LN_SF  = ln -sf
+     endif
+   endif

packages/liblz4/build.sh

@@ -11,3 +11,9 @@ TERMUX_PKG_BUILD_IN_SRC=true
 termux_step_pre_configure() {
 	TERMUX_PKG_SRCDIR+=lib
 }
+
+# Do not execute this step since on `make install` it will
+# recompile libraries & tools again.
+termux_step_make() {
+	:
+}