[clang][Fuchsia] Use unsigned int for wint_t on *-fuchsia targets (#95499)

This aligns Fuchsia targets with other similar OS targets such as
Linux.  Fuchsia's libc already uses unsigned rather than the
compiler-provided __WINT_TYPE__ macro for its wint_t typedef, so
this just makes the compiler consistent with the OS's actual ABI.
The only known manifestation of the mismatch is -Wformat warnings
for %lc no matching wint_t arguments.

The closest thing I could see to existing tests for each target's
wint_t type setting was the predefine tests that check various
macros including __WINT_TYPE__ on a per-machine and/or per-OS
basis.  While the setting is done per-OS in most of the target
implementations rather than actually varying by machine, the only
existing tests for __WINT_TYPE__ are in per-machine checks that
are also wholly or partly tagged as per-OS.  x86_64 and riscv64
tests for respective *-linux-gnu targets now check for the same
definitions in the respective *-fuchsia targets.  __WINT_TYPE__
is not among the type checked in the aarch64 tests and those lack
a section that's specifically tested for aarch64-linux-gnu; if
such is added then it can similarly be made to check for most or
all of the same value on aarch64-fuchsia as aarch64-linux-gnu.
But since the actual implementation of choosing the type is done
per-OS and not per-machine for the three machines with Fuchsia
target support, the x86 and riscv64 tests are already redundantly
testing that same code and seem sufficient.

Author: frobtech

clang/lib/Basic/Targets/OSTargets.h

@@ -868,6 +868,7 @@ class LLVM_LIBRARY_VISIBILITY FuchsiaTargetInfo : public OSTargetInfo<Target> {
 public:
   FuchsiaTargetInfo(const llvm::Triple &Triple, const TargetOptions &Opts)
       : OSTargetInfo<Target>(Triple, Opts) {
+    this->WIntType = TargetInfo::UnsignedInt;
     this->MCountName = "__mcount";
     this->TheCXXABI.set(TargetCXXABI::Fuchsia);
   }

clang/test/Preprocessor/init-x86.c

@@ -999,6 +999,7 @@
 // X32:#define __x86_64__ 1
 
 // RUN: %clang_cc1 -E -dM -ffreestanding -fgnuc-version=4.2.1 -triple=x86_64-pc-linux-gnu < /dev/null | FileCheck -match-full-lines -check-prefix X86_64-LINUX %s
+// RUN: %clang_cc1 -E -dM -ffreestanding -fgnuc-version=4.2.1 -triple=x86_64-unknown-fuchsia < /dev/null | FileCheck -match-full-lines -check-prefix X86_64-LINUX %s
 //
 // X86_64-LINUX:#define _LP64 1
 // X86_64-LINUX:#define __BIGGEST_ALIGNMENT__ 16

clang/test/Preprocessor/init.c

@@ -2527,6 +2527,8 @@
 // RUN:   | FileCheck -match-full-lines -check-prefix=RISCV64 %s
 // RUN: %clang_cc1 -E -dM -ffreestanding -fgnuc-version=4.2.1 -triple=riscv64-unknown-linux < /dev/null \
 // RUN:   | FileCheck -match-full-lines -check-prefixes=RISCV64,RISCV64-LINUX %s
+// RUN: %clang_cc1 -E -dM -ffreestanding -fgnuc-version=4.2.1 -triple=riscv64-unknown-fuchsia < /dev/null \
+// RUN:   | FileCheck -match-full-lines -check-prefixes=RISCV64 %s
 // RISCV64: #define _LP64 1
 // RISCV64: #define __ATOMIC_ACQUIRE 2
 // RISCV64: #define __ATOMIC_ACQ_REL 4