GH-47784: [C++] Patch vendored pcg library to enable msvc arm64 intrinsics (#47779)

### Rationale for this change

This change enables building Arrow C++ for Windows ARM64 with MSVC when setting `ARROW_SIMD_LEVEL` to `NONE`. This is useful to be able to build Arrow with `vcpkg` and use it as a dependency.

Setting `ARROW_SIMD_LEVEL` to `NONE` is done to disable the use of `xsimd`, which does not yet support msvc arm64 intrinsics, and is non-trivial to fix.

### What changes are included in this PR?

A patch to the vendored `pcg` library, based on imneme/pcg-cpp#99. The upstream pcg library has not been updated in the past 3 years, so this may never get merged.

### Are these changes tested?

Yes, the changes have been tested in microsoft/vcpkg#47750 (the same patch for `vcpkg`, which this change would alleviate) and in https://github.com/jgiannuzzi/ParquetSharp/actions/runs/18354286294 (a full run of the ParquetSharp CI, using this patch to build Arrow with `vcpkg`).

### Are there any user-facing changes?

Not really, unless you consider adding the ability to build Arrow on Windows ARM64 user-facing?
* GitHub Issue: #47784

Authored-by: Jonathan Giannuzzi <[email protected]>
Signed-off-by: Antoine Pitrou <[email protected]>

Author: jgiannuzzi

cpp/src/arrow/vendored/pcg/README.md

@@ -25,4 +25,5 @@ Sources are taken from git changeset ffd522e7188bef30a00c74dc7eb9de5faff90092
 Changes:
 - enclosed in `arrow_vendored` namespace
 - remove `struct arbitrary_seed` definition because of https://github.com/apache/arrow/issues/35596
+- enable MSVC ARM64 intrinsics to allow building on Windows ARM64 with Visual Studio - see https://github.com/apache/arrow/pull/47779
 

cpp/src/arrow/vendored/pcg/pcg_uint128.hpp

@@ -67,7 +67,7 @@
         #define PCG_LITTLE_ENDIAN 1
     #elif __BIG_ENDIAN__ || _BIG_ENDIAN
         #define PCG_LITTLE_ENDIAN 0
-    #elif __x86_64 || __x86_64__ || _M_X64 || __i386 || __i386__ || _M_IX86
+    #elif __x86_64 || __x86_64__ || _M_X64 || __i386 || __i386__ || _M_IX86 || _M_ARM64
         #define PCG_LITTLE_ENDIAN 1
     #elif __powerpc__ || __POWERPC__ || __ppc__ || __PPC__ \
           || __m68k__ || __mc68000__
@@ -734,7 +734,13 @@ uint_x4<UInt,UIntX2> operator*(const uint_x4<UInt,UIntX2>& a,
 
 #if PCG_64BIT_SPECIALIZATIONS
 #if defined(_MSC_VER)
+#if defined(_M_X64) || defined(_M_IX86)
 #pragma intrinsic(_umul128)
+#elif defined(_M_ARM64)
+#pragma intrinsic(__umulh)
+#else
+#error Unsupported architecture
+#endif
 #endif
 
 #if defined(_MSC_VER) || __SIZEOF_INT128__
@@ -743,8 +749,15 @@ uint_x4<UInt32,uint64_t> operator*(const uint_x4<UInt32,uint64_t>& a,
 				   const uint_x4<UInt32,uint64_t>& b)
 {
 #if defined(_MSC_VER)
+#if defined(_M_X64) || defined(_M_IX86)
     uint64_t hi;
     uint64_t lo = _umul128(a.d.v01, b.d.v01, &hi);
+#elif defined(_M_ARM64)
+    uint64_t lo = a.d.v01 * b.d.v01;
+    uint64_t hi = __umulh(a.d.v01, b.d.v01);
+#else
+#error Unsupported architecture
+#endif
 #else
     __uint128_t r = __uint128_t(a.d.v01) * __uint128_t(b.d.v01);
     uint64_t lo = uint64_t(r);