libtommath: add recipe for LibTomMath used by dropbear

* When system-libtom PACKAGECONFIG is used, both libtomcrypt and libtommath
  are used from system and we need a recipes for both.

* libtomcrypt was already added to meta-oe in langdale and PACKAGECONFIG
  was added in dropbear in:
  https://git.openembedded.org/openembedded-core/commit/?id=b7c2edd2d6ded287d8b34dd047ae84d3fd69d4c6

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>

meta-oe/recipes-support/libtommath/libtommath_1.2.0.bb

@@ -0,0 +1,23 @@
+SUMMARY = "LibTomMath is a number theoretic multiple-precision integer library"
+HOMEPAGE = "https://www.libtom.net/LibTomMath"
+SECTION = "libs"
+LICENSE = "Unlicense"
+LIC_FILES_CHKSUM = "file://LICENSE;md5=23e7e0a32e53a2b1d35f5fd9ef053402"
+
+DEPENDS = "libtool-cross"
+
+SRC_URI = "git://github.com/libtom/libtommath.git;protocol=https;branch=master"
+
+SRCREV = "6ca6898bf37f583c4cc9943441cd60dd69f4b8f2"
+
+S = "${WORKDIR}/git"
+
+EXTRA_OEMAKE = "'PREFIX=${prefix}' 'DESTDIR=${D}' 'LIBPATH=${libdir}' 'CFLAGS=${CFLAGS}'"
+
+do_compile() {
+    oe_runmake -f makefile.shared
+}
+
+do_install() {
+    oe_runmake -f makefile.shared install
+}