gdb: New component

GDB is used in wendelin.core tests:
https://lab.nexedi.com/nexedi/wendelin.core/blob/v0.13-49-g35cb144/t/tfault-run#L28

component/gdb/buildout.cfg

+# SlapOS component for GDB.
+# https://www.gnu.org/software/gdb
+
+[buildout]
+extends =
+  ../binutils/buildout.cfg
+  ../texinfo/buildout.cfg
+
+parts = gdb
+
+[gdb]
+recipe = slapos.recipe.cmmi
+shared = true
+url = http://ftp.gnu.org/gnu/gdb/gdb-9.2.tar.xz
+md5sum = db95524e554870209ab7d9f8fd8dc557
+location = @@LOCATION@@
+# gdb refuses to build in-tree -> build it inside build/
+pre-configure =
+  mkdir -p build
+configure-command =
+  cd build && ../configure
+configure-options =
+  --prefix=${:location}
+  --disable-bootstrap
+  --with-mpc=${mpc:location}
+  --with-mpfr=${mpfr:location}
+  --with-gmp=${gmp:location}
+  --with-isl=${isl:location}
+make-binary =
+make-targets = cd build && make && make install
+environment =
+  PATH=${texinfo:location}/bin:%(PATH)s