I tried on my Mac (macOS 10.14.6, Xcode 11.3.1, current develop branch, openssl 1.1.1d) and it woks fine. Below is the transcript. I 
see that your cmake output is much shorter (no C compiler listed etc.). Did you remove some lines? For such comparisons, it's 
always good to start with an empty build directory.

OpenSSL libraries are the same (1.1.1d). Just for comparison, I run the build process with "make VERBOSE=1" and extract the line 
which fails for you when linking mhttp, so maybe you can compare.

Linking mhttpd
---------------

/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++  -O2 -g -DNDEBUG -isysroot 
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk -mmacosx-version-
min=10.14 -Wl,-search_paths_first -Wl,-headerpad_max_install_names  CMakeFiles/mhttpd.dir/mhttpd.cxx.o 
CMakeFiles/mhttpd.dir/mongoose6.cxx.o CMakeFiles/mhttpd.dir/mgd.cxx.o CMakeFiles/mhttpd.dir/__/mscb/src/mscb.cxx.o  -o 
mhttpd  -L/opt/local/lib/mysql57/mysql -lmysqlclient -lz ../libmidas.a /opt/local/lib/libssl.dylib /opt/local/lib/libcrypto.dylib -lz -
L/opt/local/lib/mysql57/mysql -lmysqlclient -lz 


Here is the full transcript
-------------------------

/midas/build$ cmake ..
-- MIDAS: cmake version: 3.16.3
-- The C compiler identification is AppleClang 11.0.0.11000033
-- The CXX compiler identification is AppleClang 11.0.0.11000033
-- Check for working C compiler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/cc
-- Check for working C compiler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/cc -- 
works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: 
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++
-- Check for working CXX compiler: 
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- MIDAS: CMAKE_INSTALL_PREFIX: /midas
-- MIDAS: Found ROOT version 6.16/00
-- Found ZLIB: /opt/local/lib/libz.dylib (found version "1.2.11") 
-- MIDAS: Found ZLIB version 1.2.11
-- Found OpenSSL: /opt/local/lib/libcrypto.dylib (found version "1.1.1d")  
-- MIDAS: Found OpenSSL version 1.1.1d
-- MIDAS: Found MySQL version 5.7.26
-- MIDAS: ODBC not found
-- MIDAS: SQLITE not found
-- MIDAS: nvidia-smi not found
-- Setting default build type to "RelWithDebInfo"
-- Found Git: /usr/bin/git (found version "2.21.1 (Apple Git-122.3)") 
-- MIDAS example/experiment: MIDAS in-tree-build
-- MIDAS: Found ZLIB version 1.2.11
-- MIDAS example/experiment: Found ROOT version 6.16/00
-- Configuring done
-- Generating done
-- Build files have been written to: /midas/build
/midas/build$ make
Scanning dependencies of target rmana
Scanning dependencies of target git_revision_h
Scanning dependencies of target mfe
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[  0%] Building CXX object CMakeFiles/objlib-c-compat.dir/src/midas_c_compat.cxx.o
[  2%] Building CXX object CMakeFiles/mfe.dir/src/mfe.cxx.o
[  2%] Building CXX object CMakeFiles/mfeo.dir/src/mfe.cxx.o
[  3%] Building CXX object CMakeFiles/mana.dir/src/mana.cxx.o
[  4%] Building CXX object CMakeFiles/manao.dir/src/mana.cxx.o
[  5%] Building CXX object CMakeFiles/rmanao.dir/src/mana.cxx.o
[  6%] Building CXX object CMakeFiles/rmana.dir/src/mana.cxx.o
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[  7%] Built target objlib-c-compat
[  8%] Building CXX object CMakeFiles/objlib.dir/src/midas_cxx.cxx.o
[  8%] Linking CXX static library libmana.a
[  8%] Built target manao
[  8%] Building CXX object CMakeFiles/objlib.dir/src/odb.cxx.o
[  8%] Built target mana
[  9%] Building CXX object CMakeFiles/objlib.dir/src/device_driver.cxx.o
[  9%] Built target mfeo
[ 10%] Linking CXX static library libmfe.a
[ 11%] Building CXX object CMakeFiles/objlib.dir/src/system.cxx.o
[ 11%] Built target mfe
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[ 15%] Built target rmanao
[ 15%] Linking CXX static library librmana.a
[ 16%] Building CXX object CMakeFiles/objlib.dir/src/nullodb.cxx.o
[ 16%] Building CXX object CMakeFiles/objlib.dir/src/midasodb.cxx.o
[ 16%] Built target rmana
[ 17%] Building CXX object CMakeFiles/objlib.dir/src/mxmlodb.cxx.o
[ 18%] Building CXX object CMakeFiles/objlib.dir/src/mjsonodb.cxx.o
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[ 21%] Building CXX object CMakeFiles/objlib.dir/src/history.cxx.o
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[ 23%] Building CXX object CMakeFiles/objlib.dir/src/lz4.cxx.o
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[ 30%] Building CXX object CMakeFiles/objlib.dir/mxml/mxml.cxx.o
[ 31%] Building CXX object CMakeFiles/objlib.dir/mxml/strlcpy.cxx.o
[ 31%] Built target objlib
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[ 33%] Linking CXX shared library libmidas-shared.dylib
[ 33%] Linking CXX static library libmidas.a
[ 33%] Built target midas-shared
[ 33%] Built target midas
Scanning dependencies of target mhttpd
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[ 43%] Building CXX object progs/CMakeFiles/mjson_test.dir/mjson_test.cxx.o
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[ 44%] Building CXX object progs/CMakeFiles/odbinit.dir/odbinit.cxx.o
[ 45%] Linking CXX executable feudp
[ 45%] Built target mchart
[ 46%] Building CXX object progs/CMakeFiles/mhttpd.dir/mgd.cxx.o
[ 46%] Built target feudp
[ 46%] Building CXX object progs/CMakeFiles/mhttpd.dir/__/mscb/src/mscb.cxx.o
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[ 51%] Building CXX object progs/CMakeFiles/mh2sql.dir/mh2sql.cxx.o
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[ 51%] Building CXX object progs/CMakeFiles/odbhist.dir/odbhist.cxx.o
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[ 51%] Building CXX object progs/CMakeFiles/melog.dir/melog.cxx.o
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/midas/build$