Bug#895452: gcc-7: libquadmath is disabled for gcc 7.3.0 on powerpc64-linux-gnu

[Dennis Clarke <dclarke@blastwave.org>]

Package: gcc-7
Version: 7.3.0-15
Severity: important

Dear Maintainer,

   * What led up to the situation?

Attempt to compile a trivial code test that uses #include <quadmath.h>
as well as _Float128 datatype and quadmath_snprintf() call fails with

 fatal error: quadmath.h: No such file or directory

   * What exactly did you do (or not do) that was effective (or
     ineffective)?

Wrote a trivial piece of test code and then issued a compile :

$ gcc -mcpu=970 -mno-altivec -g -m64 -std=c99 -pedantic-errors -o s s.c 
s.c:82:10: fatal error: quadmath.h: No such file or directory
 #include <quadmath.h>
          ^~~~~~~~~~~~
compilation terminated.


   * What was the outcome of this action?

Compile can not proceed.


   * What outcome did you expect instead?

Expected a trivial to compile to generate pre-processed intermediate
file and then assembly and then an object file and then a final ELF
executable file that runs as expected.

-- System Information:
Debian Release: buster/sid
  APT prefers unreleased
  APT policy: (500, 'unreleased'), (500, 'unstable')
Architecture: ppc64

Kernel: Linux 4.15.0-2-powerpc64 (SMP w/4 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=C (charmap=ANSI_X3.4-1968), LANGUAGE=en_CA:en (charmap=ANSI_X3.4-1968)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages gcc-7 depends on:
ii  binutils      2.30-15
ii  cpp-7         7.3.0-15
ii  gcc-7-base    7.3.0-15
ii  libc6         2.27-3
ii  libcc1-0      8-20180402-1
ii  libgcc-7-dev  7.3.0-15
ii  libgcc1       1:8-20180402-1
ii  libgmp10      2:6.1.2+dfsg-3
ii  libisl19      0.19-1
ii  libmpc3       1.1.0-1
ii  libmpfr6      4.0.1-1
ii  libstdc++6    8-20180402-1
ii  zlib1g        1:1.2.8.dfsg-5

Versions of packages gcc-7 recommends:
ii  libc6-dev  2.27-3

Versions of packages gcc-7 suggests:
pn  gcc-7-doc         <none>
pn  gcc-7-locales     <none>
ii  gcc-7-multilib    7.3.0-15
pn  libasan4-dbg      <none>
pn  libatomic1-dbg    <none>
pn  libcilkrts5-dbg   <none>
pn  libgcc1-dbg       <none>
pn  libgomp1-dbg      <none>
pn  libitm1-dbg       <none>
pn  liblsan0-dbg      <none>
pn  libmpx2-dbg       <none>
pn  libquadmath0-dbg  <none>
pn  libtsan0-dbg      <none>
pn  libubsan0-dbg     <none>

-- no debconf information