when compiling with mingw64, use __mingw_aligned_malloc() and __mingw_aligned_free()

[liquidaty]

use __mingw_aligned_malloc in lieu of posix_memalign and __mingw_aligned_free in aligned_free_internal

With this change, I can successfully compile the library, and simplegrep.exe, using mingw64 (after setting env vars to point to the mingw64 toolchain) using the following steps (I'm cross-compiling from OSX, so the steps may be different / simpler on a native setup) and assuming my target PREFIX is /opt/mingw64. Note that the -DBUILD_AVX2=1 was necessary because otherwise AVX2 detection failed, and -DCMAKE_BUILD_TYPE=DEBUG fails for reasons I did not bother to investigate

cmake .. -DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY -DCMAKE_C_INCLUDE_PATH=/opt/mingw64/include -DC_INCLUDE_PATH=/opt/mingw64/include -DFAT_RUNTIME=off -DCMAKE_INSTALL_NAME_TOOL= -DBUILD_AVX2=1 -DCMAKE_BUILD_TYPE=RELEASE

# remove -search_paths_first flag which will cause minGW's gcc to error. probably this should be a separate issue and fix, but here's the quick & dirty workaround
find . -name 'link.txt' -exec sed -i.bak 's#-Wl,-search_paths_first ##g' {} \;

# build as static binary to remove dependency on non-standard DLLs (and strip symbols, though that's probably not necessary)
find . -name 'link.txt' -exec sed -i.bak 's#../lib/libhs.a#../lib/libhs.a -static -Wl,--strip-all#g' {} \;

# build simplegrep.exe
make -C examples simplegrep