[meta-oe][PATCHv2 3/3] libtomcrypt: add PACKAGECONFIG for ltm enabled by default

[Martin Jansa <martin.jansa@gmail.com>]

* enabled by default, because that's what dropbear expects and fails
  without as shown in:
  http://errors.yoctoproject.org/Errors/Details/720460/
  dropbear/2022.83-r0/crypto_desc.c:72: undefined reference to `ltm_desc'

* add comment about the LICENSE
* use EXTRA_OEMAKE

* FYI: if you need to use this in dunfell (for whatever reason e.g. to
  avoid CVE-2019-17362 in dropbear which contains bundled libtomcrypt),
  then you need to add:

  # Only needed for dunfell, fixed in kirkstone with:
  # https://git.openembedded.org/openembedded-core/commit/?h=kirkstone&id=4b308773eca7570ce5007e8f953b56252c17fdb1
  DEPENDS += "libtool-cross"
  EXTRA_OEMAKE += "'LIBTOOL=${HOST_SYS}-libtool'"

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
---
v2: inherit pkgconfig instead of explicitly using libtommath.a in EXTRALIBS
    makefile_include.mk does almost the right thing:

    ifndef EXTRALIBS
    ifneq ($(shell echo $(CFLAGS) | grep USE_LTM),)
    EXTRALIBS=$(shell PKG_CONFIG_PATH=$(LIBPATH)/pkgconfig pkg-config libtommath --libs)
    else
    ifneq ($(shell echo $(CFLAGS) | grep USE_TFM),)
    EXTRALIBS=$(shell PKG_CONFIG_PATH=$(LIBPATH)/pkgconfig pkg-config tomsfastmath --libs)
    endif
    endif
    endif

    but LIBPATH is unfortunately set to /usr/lib not SYSROOT_LIBDIR, but
    still returns '-ltommath' (as long as you don't have some strange
    libtommath on your host):
        PKG_CONFIG_PATH=/usr/lib/pkgconfig pkg-config libtommath --libs
        -ltommath

 .../libtomcrypt/libtomcrypt_1.18.2.bb         | 22 ++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/meta-oe/recipes-crypto/libtomcrypt/libtomcrypt_1.18.2.bb b/meta-oe/recipes-crypto/libtomcrypt/libtomcrypt_1.18.2.bb
index 8b73cdda85..4f6d793eb8 100644
--- a/meta-oe/recipes-crypto/libtomcrypt/libtomcrypt_1.18.2.bb
+++ b/meta-oe/recipes-crypto/libtomcrypt/libtomcrypt_1.18.2.bb
@@ -1,11 +1,18 @@
 SUMMARY = "LibTomCrypt is a public domain open source cryptographic toolkit"
 HOMEPAGE = "https://www.libtom.net/LibTomCrypt"
 SECTION = "libs"
+# Unlicense isn't very accurate for this revision, it was WTFPL in 0.18.0-rc1:
+# https://github.com/libtom/libtomcrypt/commit/77e31fb6a980212e90b9a50f116dc5a7bd91e527
+# then updated to dual license PD and WTFPL also in 0.18.0-rc1:
+# https://github.com/libtom/libtomcrypt/commit/412b2ee1fccc3a0df58f93f372c90d6d0f93bfc9
+# and then updated again to Unlicense after the 0.18.2 tag (it's only in develop branch):
+# https://github.com/libtom/libtomcrypt/commit/3630bee6fc0f73dd9c7923fd43f8ae15a2c0fb70
+# but keep using Unlicense to avoid triggering people with WTFPL license:
+# https://groups.google.com/g/libtom/c/17Z7xkECULM
+# and this comment can be removed next time libtomcrypt is updated
 LICENSE = "Unlicense"
 LIC_FILES_CHKSUM = "file://LICENSE;md5=71baacc459522324ef3e2b9e052e8180"
 
-DEPENDS += "libtool-cross"
-
 SRC_URI = "git://github.com/libtom/libtomcrypt.git;protocol=https;branch=master \
    file://CVE-2019-17362.patch \
 "
@@ -14,10 +21,19 @@ SRCREV = "7e7eb695d581782f04b24dc444cbfde86af59853"
 
 S = "${WORKDIR}/git"
 
+inherit pkgconfig
+
+PACKAGECONFIG ??= "ltm"
+PACKAGECONFIG[ltm] = ",,libtommath"
+
+CFLAGS += "${@bb.utils.contains('PACKAGECONFIG', 'ltm', '-DUSE_LTM -DLTM_DESC', '', d)}"
+
+EXTRA_OEMAKE = "'PREFIX=${prefix}' 'DESTDIR=${D}' 'LIBPATH=${libdir}' 'CFLAGS=${CFLAGS}'"
+
 do_compile() {
     oe_runmake -f makefile.shared
 }
 
 do_install() {
-    oe_runmake -f makefile.shared 'PREFIX=${prefix}' 'DESTDIR=${D}' 'LIBPATH=${libdir}' install
+    oe_runmake -f makefile.shared install
 }