[Bug c/82028] Windows x86_64 should not pass float aggregates in xmm

["jistone at redhat dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82028

--- Comment #1 from Josh Stone <jistone at redhat dot com> ---
Fedora's mingw-gcc also produces code passing through xmm0:

0000000000000000 <foo>:
   0:   55                      push   %rbp
   1:   48 89 e5                mov    %rsp,%rbp
   4:   f2 0f 11 45 10          movsd  %xmm0,0x10(%rbp)
   9:   f2 0f 10 4d 10          movsd  0x10(%rbp),%xmm1
   e:   f3 0f 7e 05 00 00 00    movq   0x0(%rip),%xmm0        # 16 <foo+0x16>
  15:   00 
  16:   66 0f 54 c1             andpd  %xmm1,%xmm0
  1a:   f2 0f 11 45 10          movsd  %xmm0,0x10(%rbp)
  1f:   f2 0f 10 45 10          movsd  0x10(%rbp),%xmm0
  24:   5d                      pop    %rbp
  25:   c3                      retq   

$ x86_64-w64-mingw32-gcc -v
Using built-in specs.
COLLECT_GCC=x86_64-w64-mingw32-gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-w64-mingw32/7.1.0/lto-wrapper
Target: x86_64-w64-mingw32
Configured with: ../configure --prefix=/usr --bindir=/usr/bin
--includedir=/usr/include --mandir=/usr/share/man --infodir=/usr/share/info
--datadir=/usr/share --build=x86_64-redhat-linux-gnu
--host=x86_64-redhat-linux-gnu --with-gnu-as --with-gnu-ld --verbose
--without-newlib --disable-multilib --disable-plugin --with-system-zlib
--disable-nls --without-included-gettext --disable-win32-registry
--enable-languages=c,c++,objc,obj-c++,fortran
--with-bugurl=http://bugzilla.redhat.com/bugzilla --with-cloog
--enable-threads=posix --enable-libgomp --target=x86_64-w64-mingw32
--with-sysroot=/usr/x86_64-w64-mingw32/sys-root
--with-gxx-include-dir=/usr/x86_64-w64-mingw32/sys-root/mingw/include/c++
Thread model: posix
gcc version 7.1.0 20170502 (Fedora MinGW 7.1.0-1.fc26) (GCC)