stage1: work around LLVM's buggy fma lowering

 * move fmaq from freestanding libc to compiler_rt, unconditionally
   exported weak_odr.
 * stage1: add fmaf, fmal, fmaq as symbols that compiler-rt might
   generate calls to.
 * stage1: lower `@mulAdd` directly to a call to `fmaq` instead of to
   the LLVM intrinsic because LLVM will lower it to `fmal` even when the
   target's `long double` is not equivalent to `f128`.

This commit is intended to fix the test suite which is failing on the
previous commit.

1 files changed, 6 insertions, 0 deletions

diff --git a/lib/std/special/compiler_rt.zig b/lib/std/special/compiler_rt.zig
index ce3373abac..1b3e80ed12 100644
--- a/lib/std/special/compiler_rt.zig
+++ b/lib/std/special/compiler_rt.zig
@@ -616,9 +616,15 @@ comptime {
         @export(__mulodi4, .{ .name = "__mulodi4", .linkage = linkage });
 
         _ = @import("compiler_rt/atomics.zig");
+
+        @export(fmaq, .{ .name = "fmaq", .linkage = linkage });
     }
 }
 
+fn fmaq(a: f128, b: f128, c: f128) callconv(.C) f128 {
+    return std.math.fma(f128, a, b, c);
+}
+
 // Avoid dragging in the runtime safety mechanisms into this .o file,
 // unless we're trying to test this file.
 pub fn panic(msg: []const u8, error_return_trace: ?*std.builtin.StackTrace) noreturn {