improve min_mac_version support; bump to 10.15

CMakeLists.txt

@@ -16,6 +16,9 @@ set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_EXTENSIONS OFF)
 
+# Set max os target version.
+set(CMAKE_OSX_DEPLOYMENT_TARGET 10.15)
+
 # Default Build Type to be Release
 if(NOT CMAKE_BUILD_TYPE)
   set(CMAKE_BUILD_TYPE "Release" CACHE STRING

makefiles/Makefile.third_party.unix.mk

@@ -220,7 +220,7 @@ dependencies/install/lib/libprotobuf.a: $(PROTOBUF_SRCDIR) | dependencies/instal
     -DBUILD_TESTING=OFF \
     -Dprotobuf_BUILD_TESTS=OFF \
     -Dprotobuf_BUILD_EXAMPLES=OFF \
-    -DCMAKE_CXX_FLAGS="$(MAC_VERSION)" \
+    -DCMAKE_OSX_DEPLOYMENT_TARGET="$(MAC_MIN_VERSION)" \
     -DCMAKE_INSTALL_PREFIX=../../install && \
   $(CMAKE) --build build_cmake --config Release -v -- -j4 && \
   $(CMAKE) --build build_cmake --config Release --target install
@@ -289,7 +289,7 @@ dependencies/install/lib/libabsl.a: dependencies/sources/abseil-cpp-$(ABSL_TAG)
     -DCMAKE_PREFIX_PATH="$(OR_TOOLS_TOP)/dependencies/install" \
     -DBUILD_SHARED_LIBS=OFF \
     -DBUILD_STATIC_LIBS=ON \
-    -DCMAKE_CXX_FLAGS="$(MAC_VERSION)" \
+    -DCMAKE_OSX_DEPLOYMENT_TARGET="$(MAC_MIN_VERSION)" \
     -DBUILD_TESTING=OFF \
     -DCMAKE_INSTALL_PREFIX=../../install && \
   $(CMAKE) --build build_cmake --config Release -v -- -j4 && \
@@ -622,7 +622,7 @@ dependencies/install/lib/libscip.a: $(SCIP_SRCDIR) | dependencies/install
     -DSHARED=OFF \
     -DBUILD_STATIC_LIBS=ON \
     -DBUILD_TESTING=OFF \
-    -DCMAKE_CXX_FLAGS="$(MAC_VERSION)" \
+    -DCMAKE_OSX_DEPLOYMENT_TARGET="$(MAC_MIN_VERSION)" \
     -DREADLINE=OFF \
     -DGMP=OFF \
     -DPAPILO=OFF \