freestanding libc: don't rely on compiler_rt symbols we don't have yet

Previous commit made fmal depend on __extendxftf2 and __trunctfxf2 but
we don't have implementations of those yet.

lib/std/special/c_stage1.zig

@@ -5,6 +5,7 @@ const isNan = std.math.isNan;
 const native_arch = builtin.cpu.arch;
 const native_abi = builtin.abi;
 const native_os = builtin.os.tag;
+const long_double_is_f128 = builtin.target.longDoubleIsF128();
 
 const is_wasm = switch (native_arch) {
     .wasm32, .wasm64 => true,
@@ -657,6 +658,9 @@ export fn ceil(x: f64) f64 {
 }
 
 export fn fmal(a: c_longdouble, b: c_longdouble, c: c_longdouble) c_longdouble {
+    if (!long_double_is_f128) {
+        @panic("TODO implement this");
+    }
     return math.fma(c_longdouble, a, b, c);
 }
 

lib/std/special/compiler_rt.zig

@@ -18,6 +18,8 @@ const strong_linkage = if (is_test)
 else
     std.builtin.GlobalLinkage.Strong;
 
+const long_double_is_f128 = builtin.target.longDoubleIsF128();
+
 comptime {
     const __extenddftf2 = @import("compiler_rt/extendXfYf2.zig").__extenddftf2;
     @export(__extenddftf2, .{ .name = "__extenddftf2", .linkage = linkage });
@@ -75,6 +77,15 @@ comptime {
     }
 
     if (!builtin.zig_is_stage2) {
+        if (!long_double_is_f128) {
+            // TODO implement these
+            //const __extendxftf2 = @import("compiler_rt/extendXfYf2.zig").__extendxftf2;
+            //@export(__extendxftf2, .{ .name = "__extendxftf2", .linkage = linkage });
+
+            //const __trunctfxf2 = @import("compiler_rt/truncXfYf2.zig").__trunctfxf2;
+            //@export(__trunctfxf2, .{ .name = "__trunctfxf2", .linkage = linkage });
+        }
+
         switch (arch) {
             .i386,
             .x86_64,

lib/std/special/compiler_rt/extendXfYf2.zig

@@ -22,6 +22,11 @@ pub fn __extendhftf2(a: u16) callconv(.C) f128 {
     return extendXfYf2(f128, f16, a);
 }
 
+pub fn __extendxftf2(a: c_longdouble) callconv(.C) f128 {
+    _ = a;
+    @panic("TODO implement");
+}
+
 pub fn __aeabi_h2f(arg: u16) callconv(.AAPCS) f32 {
     @setRuntimeSafety(false);
     return @call(.{ .modifier = .always_inline }, __extendhfsf2, .{arg});

lib/std/special/compiler_rt/truncXfYf2.zig

@@ -20,6 +20,11 @@ pub fn __trunctfdf2(a: f128) callconv(.C) f64 {
     return @call(.{ .modifier = .always_inline }, truncXfYf2, .{ f64, f128, a });
 }
 
+pub fn __trunctfxf2(a: f128) callconv(.C) c_longdouble {
+    _ = a;
+    @panic("TODO implement");
+}
+
 pub fn __truncdfsf2(a: f64) callconv(.C) f32 {
     return @call(.{ .modifier = .always_inline }, truncXfYf2, .{ f32, f64, a });
 }

lib/std/target.zig

@@ -1712,6 +1712,13 @@ pub const Target = struct {
             else => ".X",
         };
     }
+
+    pub inline fn longDoubleIsF128(target: Target) bool {
+        return switch (target.cpu.arch) {
+            .riscv64, .aarch64, .aarch64_be, .aarch64_32, .s390x, .mips64, .mips64el => true,
+            else => false,
+        };
+    }
 };
 
 test {