De-duplicate and improve definition of core::ffi::c_char

Instead of having a list of unsigned char targets for each OS, follow the
logic Clang uses and instead set the value based on architecture with
a special case for Darwin and Windows operating systems. This makes it
easier to support new operating systems targeting Arm/AArch64 without
having to modify this config statement for each new OS. The new list does
not quite match Clang since I noticed a few bugs in the Clang
implementation (llvm/llvm-project#115957).

Author: arichardson

library/core/src/ffi/mod.rs

@@ -92,56 +92,46 @@ pub type c_ssize_t = isize;
 mod c_char_definition {
     cfg_if! {
         // These are the targets on which c_char is unsigned.
-        if #[cfg(any(
-            all(
-                target_os = "linux",
-                any(
-                    target_arch = "aarch64",
-                    target_arch = "arm",
-                    target_arch = "hexagon",
-                    target_arch = "powerpc",
-                    target_arch = "powerpc64",
-                    target_arch = "s390x",
-                    target_arch = "riscv64",
-                    target_arch = "riscv32",
-                    target_arch = "csky"
-                )
+        // See isSignedCharDefault() in clang/lib/Driver/ToolChains/Clang.cpp
+        // PowerPC uses unsigned char for all targets except Darwin.
+        // Arm/AArch64 uses unsigned char except for Darwin and Windows targets
+        if #[cfg(all(
+            any(
+                target_os = "ios",
+                target_os = "macos",
+                target_os = "tvos",
+                target_os = "visionos",
+                target_os = "watchos",
             ),
-            all(target_os = "android", any(target_arch = "aarch64", target_arch = "arm")),
-            all(target_os = "l4re", target_arch = "x86_64"),
-            all(
-                any(target_os = "freebsd", target_os = "openbsd", target_os = "rtems"),
-                any(
-                    target_arch = "aarch64",
-                    target_arch = "arm",
-                    target_arch = "powerpc",
-                    target_arch = "powerpc64",
-                    target_arch = "riscv64"
-                )
+            any(
+                target_arch = "aarch64",
+                target_arch = "arm",
+                target_arch = "powerpc",
+                target_arch = "powerpc64",
             ),
-            all(
-                target_os = "netbsd",
-                any(
-                    target_arch = "aarch64",
-                    target_arch = "arm",
-                    target_arch = "powerpc",
-                    target_arch = "riscv64"
-                )
-            ),
-            all(
-                target_os = "vxworks",
-                any(
-                    target_arch = "aarch64",
-                    target_arch = "arm",
-                    target_arch = "powerpc64",
-                    target_arch = "powerpc"
-                )
-            ),
-            all(
-                target_os = "fuchsia",
-                any(target_arch = "aarch64", target_arch = "riscv64")
+        ))] {
+            pub type c_char = i8;
+        } else if #[cfg(all(
+            target_os = "windows",
+            any(
+                target_arch = "aarch64",
+                target_arch = "arm",
+                target_arch = "arm64ec"
             ),
-            all(target_os = "nto", target_arch = "aarch64"),
+        ))] {
+            pub type c_char = i8;
+        } else if #[cfg(any(
+            target_arch = "aarch64",
+            target_arch = "arm",
+            target_arch = "csky",
+            target_arch = "hexagon",
+            target_arch = "msp430",
+            target_arch = "powerpc",
+            target_arch = "powerpc64",
+            target_arch = "riscv64",
+            target_arch = "riscv32",
+            target_arch = "s390x",
+            target_arch = "xtensa",
             target_os = "horizon",
             target_os = "aix",
         ))] {