$ makepkg
==> Making package: arm-none-eabi-gcc 9.1.0-1 (Mon 15 Jul 2019 09:03:51 PM CEST)
==> Checking runtime dependencies...
==> Checking buildtime dependencies...
==> Retrieving sources...
  -> Found gcc-9.1.0.tar.xz
  -> Found gcc-9.1.0.tar.xz.sig
  -> Found isl-0.21.tar.bz2
==> Validating source files with sha256sums...
    gcc-9.1.0.tar.xz ... Passed
    gcc-9.1.0.tar.xz.sig ... Skipped
    isl-0.21.tar.bz2 ... Passed
==> Verifying source file signatures with gpg...
    gcc-9.1.0.tar.xz ... Passed
==> Extracting sources...
  -> Extracting gcc-9.1.0.tar.xz with bsdtar
==> Starting prepare()...
==> Starting build()...
checking build system type... armv6l-unknown-linux-gnueabihf
checking host system type... armv6l-unknown-linux-gnueabihf
checking target system type... arm-none-eabi
checking for a BSD-compatible install... /usr/bin/install -c
checking whether ln works... yes
checking whether ln -s works... yes
checking for a sed that does not truncate output... /usr/bin/sed
checking for gawk... gawk
checking for libatomic support... no
checking for libitm support... no
checking for libsanitizer support... no
checking for libvtv support... no
checking for libhsail-rt support... no
checking for libphobos support... no
checking for gcc... gcc
checking whether the C compiler works... yes
checking for C compiler default output file name... a.out
checking for suffix of executables... 
checking whether we are cross compiling... no
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether gcc accepts -g... yes
checking for gcc option to accept ISO C89... none needed
checking for g++... g++
checking whether we are using the GNU C++ compiler... yes
checking whether g++ accepts -g... yes
checking whether g++ accepts -static-libstdc++ -static-libgcc... yes
checking for gnatbind... no
checking for gnatmake... no
checking whether compiler driver understands Ada... no
checking how to compare bootstrapped objects... cmp --ignore-initial=16 $$f1 $$f2
checking for objdir... .libs
checking for the correct version of gmp.h... yes
checking for the correct version of mpfr.h... yes
checking for the correct version of mpc.h... yes
checking for the correct version of the gmp/mpfr/mpc libraries... yes
checking for isl 0.15 or later... no
required isl version is 0.15 or later
configure: error: Unable to find a usable isl.  See config.log for details.
==> ERROR: A failure occurred in build().
    Aborting...