configure: Allow log2 with MSVC 2013 onwards.

Only MSVC 2010 in x64 mode, in the static msvcrt, had a
stray log2 function (which wasn't available in the headers).

MSVC 2013 has got a proper log2 function though.

Signed-off-by: Martin Storsjö <martin@martin.st>

configure

@@ -1744,8 +1744,6 @@ fast_unaligned_if_any="aarch64 ppc x86"
 simd_align_16_if_any="altivec neon sse"
 
 # system capabilities
-log2_deps="!libc_msvcrt"
-
 symver_if_any="symver_asm_label symver_gnu_asm"
 valgrind_backtrace_deps="!optimizations valgrind_valgrind_h"
 
@@ -4563,6 +4561,8 @@ elif enabled_any msvc icl; then
         # not supported (build will fail)
         disable inline_asm
     fi
+    # msvcrt10 x64 incorrectly enables log2, only msvcrt12 (MSVC 2013) onwards actually has log2.
+    check_cpp_condition crtversion.h "_VC_CRT_MAJOR_VERSION >= 12" || disable log2
 fi
 
 case $as_type in