Compilation fails on FreeBSD < 12

[past-due]

Using commit: aeffa9b

FreeBSD 11.4:
-- The C compiler identification is Clang 10.0.0
-- The CXX compiler identification is Clang 10.0.0

FAILED: 3rdparty/zlib-ng/CMakeFiles/zlib.dir/zutil.c.o 
/usr/bin/cc -DHAVE_BUILTIN_CTZ -DHAVE_BUILTIN_CTZLL -DHAVE_VISIBILITY_HIDDEN -DHAVE_VISIBILITY_INTERNAL -DUNALIGNED64_OK -DUNALIGNED_OK -DWITH_GZFILEOP -DX86_AVX2 -DX86_AVX2_ADLER32 -DX86_AVX_CHUNKSET -DX86_FEATURES -DX86_PCLMULQDQ_CRC -DX86_SSE2 -DX86_SSE2_CHUNKSET -DX86_SSE2_SLIDEHASH -DX86_SSE42_CMP_STR -DX86_SSE42_CRC_HASH -DX86_SSE42_CRC_INTRIN -DX86_SSSE3 -DX86_SSSE3_ADLER32 -D_LARGEFILE64_SOURCE=1 -D__USE_LARGEFILE64 -I3rdparty/zlib-ng -I../../3rdparty/zlib-ng -fstack-protector-strong -Wall -Wno-implicit-fallthrough -O2 -g -DNDEBUG -fPIC -std=c99 -MD -MT 3rdparty/zlib-ng/CMakeFiles/zlib.dir/zutil.c.o -MF 3rdparty/zlib-ng/CMakeFiles/zlib.dir/zutil.c.o.d -o 3rdparty/zlib-ng/CMakeFiles/zlib.dir/zutil.c.o -c ../../3rdparty/zlib-ng/zutil.c
In file included from ../../3rdparty/zlib-ng/zutil.c:8:
In file included from ../../3rdparty/zlib-ng/zutil_p.h:11:
/usr/include/malloc.h:3:2: error: "<malloc.h> has been replaced by <stdlib.h>"
#error "<malloc.h> has been replaced by <stdlib.h>"
 ^
In file included from ../../3rdparty/zlib-ng/zutil.c:8:
../../3rdparty/zlib-ng/zutil_p.h:21:20: warning: implicit declaration of function 'memalign' is invalid in C99 [-Wimplicit-function-declaration]
    return (void *)memalign(64, size);
                   ^
../../3rdparty/zlib-ng/zutil_p.h:21:12: warning: cast to 'void *' from smaller integer type 'int' [-Wint-to-void-pointer-cast]
    return (void *)memalign(64, size);
           ^
2 warnings and 1 error generated.

Although interestingly, zero issues on FreeBSD 12.2. In case it matters (for the warnings), 12.2 has a slightly newer version of Clang:
-- The C compiler identification is Clang 10.0.1
-- The CXX compiler identification is Clang 10.0.1

[past-due]

Reference: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=155429

On Linux/glibc <malloc.h> defines extensions (e.g., memalign, malloc_usable_size, mallinfo) that FreeBSD provides via <malloc_np.h> (e.g., *allocx, malloc_usable_size, mallctl) while similar to upstream jemalloc.

Reference: https://svnweb.freebsd.org/base?view=revision&revision=360984

It may be desirable to detect FreeBSD, and do something like:

  #ifdef __APPLE__
  #  include <stdlib.h>
+ #elif defined(__FreeBSD__)
+ #  include <stdlib.h>
+ #  include <malloc_np.h>
  #else
  #  include <malloc.h>
  #endif

[Dead2]

It may be desirable to detect FreeBSD, and do something like:

  #ifdef __APPLE__
  #  include <stdlib.h>
+ #elif defined(__FreeBSD__)
+ #  include <stdlib.h>
+ #  include <malloc_np.h>
  #else
  #  include <malloc.h>
  #endif

I guess this would also need an #elif defined(__FreeBSD__) to use __posix_memalign.

This sounds like something I could pull as a fix without waiting for a future stable release branch, since it is a minimal change that is (very) unlikely to have unknown effects on other platforms.
#884 is turning into a bigger refactoring PR that I will have to postpone merging until we open the develop branch for developing the next feature version.

[Dead2]

This should be fixed in 2.0.2.