On WIN32, fix compile errors on non MSVC compilers

Author: Rt39

src/libFLAC/CMakeLists.txt

@@ -21,6 +21,9 @@ if(FLAC__CPU_X86_64 OR FLAC__CPU_IA32)
     if(WITH_AVX AND MSVC)
         set_source_files_properties(fixed_intrin_avx2.c lpc_intrin_avx2.c stream_encoder_intrin_avx2.c lpc_intrin_fma.c PROPERTIES COMPILE_FLAGS /arch:AVX2)
     endif()
+    if(WITH_AVX AND WIN32 AND NOT MSVC)
+        set_source_files_properties(fixed_intrin_avx2.c lpc_intrin_avx2.c stream_encoder_intrin_avx2.c lpc_intrin_fma.c PROPERTIES COMPILE_FLAGS -mavx2)
+    endif()
 else()
     check_cpu_arch_arm64(FLAC__CPU_ARM64)
     if(FLAC__CPU_ARM64)

src/share/getopt/getopt.c

@@ -221,7 +221,7 @@ static char *posixly_correct;
 /* Avoid depending on library functions or files
    whose names are inconsistent.  */
 
-#ifndef getenv
+#if !defined(getenv) && !(defined(__clang__) && defined(_MSC_VER))
 extern char *getenv (const char * name);
 #endif