target/i386: floatx80: avoid compound literals in static initializers

target/i386: floatx80: avoid compound literals in static initializers

Quoting ISO C99 6.7.8p4, "All the expressions in an initializer for an
object that has static storage duration shall be constant expressions or
string literals".

The compound literal produced by the make_floatx80() macro is not such a
constant expression, per 6.6p7-9. (An implementation may accept it,
according to 6.6p10, but is not required to.)

Therefore using "floatx80_zero" and make_floatx80() for initializing
"f2xm1_table" and "fpatan_table" is not portable. And gcc-4.8 in RHEL-7.6
actually chokes on them:

> target/i386/fpu_helper.c:871:5: error: initializer element is not constant
>      { make_floatx80(0xbfff, 0x8000000000000000ULL),
>      ^

We've had the make_floatx80_init() macro for this purpose since commit
3bf7e40ab914 ("softfloat: fix for C99", 2012-03-17), so let's use that
macro again.

Fixes: eca30647fc0 ("target/i386: reimplement f2xm1 using floatx80 operations")
Fixes: ff57bb7b632 ("target/i386: reimplement fpatan using floatx80 operations")
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Joseph Myers <joseph@codesourcery.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>
Link: https://lists.gnu.org/archive/html/qemu-devel/2017-08/msg06566.html
Link: https://lists.gnu.org/archive/html/qemu-devel/2020-07/msg04714.html
Message-Id: <20200716144251.23004-1-lersek@redhat.com>
Message-Id: <20200724064509.331-8-alex.bennee@linaro.org>