Issue with executing a.out file (C++) MacO

I just updated to Sierra and it seems my compiler fell apart for some reason.

The code I wrote worked fine before the update, so I'm sure its not an issue there but now it just isn't working what so ever when I try to execute it.

Here is the output.

$ g++ source.cpp
$ ./a.out
dyld: mach-o, but built for simulator (not macOS)
Abort trap: 6

Running G++ with verbose for @NulledPointer

$ g++ --verbose source.cpp
Apple LLVM version 8.0.0 (clang-800.0.38)
Target: x86_64-apple-darwin16.1.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
 "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang" -cc1 -triple x86_64-apple-ios7.0.0 -Wdeprecated-objc-isa-usage -Werror=deprecated-objc-isa-usage -Werror=implicit-function-declaration -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name source.cpp -mrelocation-model pic -pic-level 2 -mthread-model posix -mdisable-fp-elim -masm-verbose -munwind-tables -target-cpu core2 -target-linker-version 274.1 -v -dwarf-column-info -debugger-tuning=lldb -resource-dir /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/clang/8.0.0 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator10.0.sdk -stdlib=libc++ -Wno-error -fdeprecated-macro -fdebug-compilation-dir /Users/USERNAME/FILE_DIRECTORY/ -ferror-limit 19 -fmessage-length 130 -stack-protector 1 -fblocks -fobjc-runtime=ios-7.0.0 -fencode-extended-block-signature -fcxx-exceptions -fexceptions -fmax-type-align=16 -fdiagnostics-show-option -fcolor-diagnostics -o /var/folders/kr/tvqfrgdx2w32m0c9fq96zddc0000gn/T/source-355902.o -x c++ source.cpp
clang -cc1 version 8.0.0 (clang-800.0.38) default target x86_64-apple-darwin16.1.0
ignoring nonexistent directory "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator10.0.sdk/usr/include/c++/v1"
ignoring nonexistent directory "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator10.0.sdk/usr/local/include"
#include "..." search starts here:
#include <...> search starts here:
 /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1
 /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/clang/8.0.0/include
 /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include
 /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator10.0.sdk/usr/include
 /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator10.0.sdk/System/Library/Frameworks (framework directory)
 /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator10.0.sdk/Library/Frameworks (framework directory)
End of search list.
 "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld" -demangle -dynamic -arch x86_64 -ios_simulator_version_min 7.0.0 -syslibroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator10.0.sdk -o a.out /var/folders/kr/tvqfrgdx2w32m0c9fq96zddc0000gn/T/source-355902.o -lc++ -lSystem /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/clang/8.0.0/lib/darwin/libclang_rt.ios.a

Error from running that command NulledPointer posted.

clang: warning: no such sysroot directory: '/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.11.sdk'
clang: warning: using sysroot for 'MacOSX' but targeting 'iPhone'
In file included from source.cpp:10:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/iostream:38:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/ios:215:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/iosfwd:90:10: fatal error: 
      'wchar.h' file not found
#include <wchar.h>  // for mbstate_t
         ^
1 error generated.

There are multiple options:

Try installing missing tools (if any) using xcode-select --install and try compiling. If that fails,
Try running gcc -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.11.sdk source.cpp. This obviously assuming you have SDK installed in that location. Replace with whatever location exist there.