bitfields: promote to signed int

For integer promotion with for example arithmetics or
expr_cond (x ? y : z), integral types need to be promoted
to signed if they fit.

According to latest standards, this also applies to bit-field
types taking into account their specific width.

In tcc, VT_BITFIELD set means width < original type width
Field-widths between 33 and 63 are promoted to signed long long
accordingly.

    struct { unsigned long long ullb:35; } s = { 1 };
    #define X (s.ullb - 2)

    int main (void)
    {
        long long Y = X;
        printf("%d %016llx %016llx\n", X < 0, -X, -Y);
        return 0;
    }

Results:
    GCC 4.7 : 0 0000000000000001 FFFFFFF800000001
    MSVC    : 1 0000000000000001 0000000000000001
    TCC     : 1 0000000000000001 0000000000000001

Also, gcc would promote long long bitfields of size < 32
to int as well.  Example:

    struct { unsigned long long x:20; } t = { 123 };
    /* with gcc: */ printf("%d %d\n", t.x, 456);
    /* with tcc: */ printf("%lld %d\n", t.x, 456);

1 files changed, 46 insertions, 0 deletions

diff --git a/tests/tests2/93_integer_promotion.expect b/tests/tests2/93_integer_promotion.expect
new file mode 100644
index 0000000..34b9c14
--- /dev/null
+++ b/tests/tests2/93_integer_promotion.expect
@@ -0,0 +1,46 @@
+   signed : s.ub
+ unsigned : s.u
+   signed : s.ullb
+ unsigned : s.ull
+   signed : s.c
+
+   signed : (1 ? s.ub : 1)
+ unsigned : (1 ? s.u : 1)
+   signed : (1 ? s.ullb : 1)
+ unsigned : (1 ? s.ull : 1)
+   signed : (1 ? s.c : 1)
+
+   signed : s.ub << 1
+ unsigned : s.u << 1
+   signed : s.ullb << 1
+ unsigned : s.ull << 1
+   signed : s.c << 1
+
+   signed : +s.ub
+ unsigned : +s.u
+   signed : +s.ullb
+ unsigned : +s.ull
+   signed : +s.c
+
+   signed : -s.ub
+ unsigned : -s.u
+   signed : -s.ullb
+ unsigned : -s.ull
+   signed : -s.c
+
+   signed : ~s.ub
+ unsigned : ~s.u
+   signed : ~s.ullb
+ unsigned : ~s.ull
+   signed : ~s.c
+
+   signed : !s.ub
+   signed : !s.u
+   signed : !s.ullb
+   signed : !s.ull
+   signed : !s.c
+
+ unsigned : +(unsigned)s.ub
+ unsigned : -(unsigned)s.ub
+ unsigned : ~(unsigned)s.ub
+   signed : !(unsigned)s.ub