Add a span to `CompilerBuiltinsCannotCall`

Currently, this error emit a diagnostic with no context like:

    error: `compiler_builtins` cannot call functions through upstream monomorphizations; encountered invalid call from `<math::libm::support::hex_float::Hexf<i32> as core::fmt::LowerHex>::fmt` to `core::fmt::num::<impl core::fmt::LowerHex for i32>::fmt`

With this change, it at least usually points to the problematic
function:

    error: `compiler_builtins` cannot call functions through upstream monomorphizations; encountered invalid call from `<math::libm::support::hex_float::Hexf<i32> as core::fmt::LowerHex>::fmt` to `core::fmt::num::<impl core::fmt::LowerHex for i32>::fmt`
       --> src/../libm/src/math/support/hex_float.rs:270:5
        |
    270 |     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        |

1 files changed, 2 insertions, 0 deletions

diff --git a/compiler/rustc_codegen_ssa/src/errors.rs b/compiler/rustc_codegen_ssa/src/errors.rs
index 3ddbe4aeeec..5e25de02a77 100644
--- a/compiler/rustc_codegen_ssa/src/errors.rs
+++ b/compiler/rustc_codegen_ssa/src/errors.rs
@@ -1180,6 +1180,8 @@ pub(crate) struct ErrorCreatingRemarkDir {
 pub struct CompilerBuiltinsCannotCall {
     pub caller: String,
     pub callee: String,
+    #[primary_span]
+    pub span: Span,
 }
 
 #[derive(Diagnostic)]