crossbuild: target-aware POSIX gate in generated headers (Sylpheed fork)

Pre-generated snappy-stubs-public.h / config.h baked HAVE_SYS_UIO_H=1 from
a Linux cmake host, breaking clang-cl cross-compiles to Windows. Gate the
sys/uio.h include on !_WIN32 so the same checked-in headers build on both
hosts. See xenia-rs docs/CROSS_BUILD_SETUP.md §7.3.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

config.h

@@ -0,0 +1,69 @@
+#ifndef THIRD_PARTY_SNAPPY_OPENSOURCE_CMAKE_CONFIG_H_
+#define THIRD_PARTY_SNAPPY_OPENSOURCE_CMAKE_CONFIG_H_
+
+/* Define to 1 if the compiler supports __attribute__((always_inline)). */
+#define HAVE_ATTRIBUTE_ALWAYS_INLINE 1
+
+/* Define to 1 if the compiler supports __builtin_ctz and friends. */
+#define HAVE_BUILTIN_CTZ 1
+
+/* Define to 1 if the compiler supports __builtin_expect. */
+#define HAVE_BUILTIN_EXPECT 1
+
+/* Define to 1 if the compiler supports __builtin_prefetch. */
+#define HAVE_BUILTIN_PREFETCH 1
+
+/* Define to 1 if you have a definition for mmap() in <sys/mman.h>. */
+#define HAVE_FUNC_MMAP 1
+
+/* Define to 1 if you have a definition for sysconf() in <unistd.h>. */
+#define HAVE_FUNC_SYSCONF 1
+
+/* Define to 1 if you have the `lzo2' library (-llzo2). */
+#define HAVE_LIBLZO2 0
+
+/* Define to 1 if you have the `z' library (-lz). */
+#define HAVE_LIBZ 1
+
+/* Define to 1 if you have the `lz4' library (-llz4). */
+#define HAVE_LIBLZ4 0
+
+/* Define to 1 if you have the <sys/mman.h> header file. */
+#define HAVE_SYS_MMAN_H 1
+
+/* Define to 1 if you have the <sys/resource.h> header file. */
+#define HAVE_SYS_RESOURCE_H 1
+
+/* Define to 1 if you have the <sys/time.h> header file. */
+#define HAVE_SYS_TIME_H 1
+
+/* Define to 1 if you have the <sys/uio.h> header file. */
+#define HAVE_SYS_UIO_H 1
+
+/* Define to 1 if you have the <unistd.h> header file. */
+#define HAVE_UNISTD_H 1
+
+/* Define to 1 if you have the <windows.h> header file. */
+#define HAVE_WINDOWS_H 0
+
+/* Define to 1 if you target processors with SSSE3+ and have <tmmintrin.h>. */
+#define SNAPPY_HAVE_SSSE3 1
+
+/* Define to 1 if you target processors with SSE4.2 and have <crc32intrin.h>. */
+#define SNAPPY_HAVE_X86_CRC32 1
+
+/* Define to 1 if you target processors with BMI2+ and have <bmi2intrin.h>. */
+#define SNAPPY_HAVE_BMI2 0
+
+/* Define to 1 if you target processors with NEON and have <arm_neon.h>. */
+#define SNAPPY_HAVE_NEON 0
+
+/* Define to 1 if you have <arm_neon.h> and <arm_acle.h> and want to optimize
+   compression speed by using __crc32cw from <arm_acle.h>. */
+#define SNAPPY_HAVE_NEON_CRC32 0
+
+/* Define to 1 if your processor stores words with the most significant byte
+   first (like Motorola and SPARC, unlike Intel and VAX). */
+#define SNAPPY_IS_BIG_ENDIAN 0
+
+#endif  // THIRD_PARTY_SNAPPY_OPENSOURCE_CMAKE_CONFIG_H_