Error messages each time I compile a sketch...

Hello !
I am pretty new in using Arduino.... and every time I want to compile a sketch the process doesn't go through... Everytime this type of error messages appear, as if something is missing but I cannot find what.
I have uninstall and re-install Arduino several times, but the situation remain the same. My OS is 10.7.5... but I don't think it is related to these messages....

I would be very grateful if someone could help me to find the solution because I cannot work at all with Arduino for the moment....

Thanks a lot !

Here is two examples of error messages I have :

FIRST ONE =

Arduino: 1.8.3 (Mac OS X), Board: "Arduino/Genuino Uno"

/Applications/Arduino.app/Contents/Java/hardware/tools/avr/bin/../lib/gcc/avr/4.9.2/../../../../avr/bin/ld: /Applications/Arduino.app/Contents/Java/hardware/tools/avr/bin/../libexec/gcc/avr/4.9.2/liblto_plugin.so: error loading plugin: dlopen(/Applications/Arduino.app/Contents/Java/hardware/tools/avr/bin/../libexec/gcc/avr/4.9.2/liblto_plugin.so, 2): Symbol not found: _environ
Referenced from: /Applications/Arduino.app/Contents/Java/hardware/tools/avr/bin/../libexec/gcc/avr/4.9.2/liblto_plugin.so
Expected in: /usr/lib/libSystem.B.dylib

collect2: error: ld returned 1 exit status
exit status 1
Error compiling for board Arduino/Genuino Uno.

This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.

Second ONE =

Arduino: 1.8.3 (Mac OS X), Board: "Arduino/Genuino Uno"

/Applications/Arduino.app/Contents/Java/hardware/tools/avr/bin/../lib/gcc/avr/4.9.2/../../../../avr/bin/ld: /Applications/Arduino.app/Contents/Java/hardware/tools/avr/bin/../libexec/gcc/avr/4.9.2/liblto_plugin.so: error loading plugin: dlopen(/Applications/Arduino.app/Contents/Java/hardware/tools/avr/bin/../libexec/gcc/avr/4.9.2/liblto_plugin.so, 2): Symbol not found: _environ
Referenced from: /Applications/Arduino.app/Contents/Java/hardware/tools/avr/bin/../libexec/gcc/avr/4.9.2/liblto_plugin.so
Expected in: /usr/lib/libSystem.B.dylib

collect2: error: ld returned 1 exit status
exit status 1
Error compiling for board Arduino/Genuino Uno.

This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.

I don't know MACs but it would probably help if you edit your Original Post and add "on a MAC" into the title.

...R

Looks like an installation problem. First thing to try is a re-install.

A bunch of people have had IDE problems, including IDE crashes and bizarre compile errors, when they install a new version of the IDE. At least some of those problems seem to be caused by incompatible executables and preference files that the IDE saves outside the IDE installation directory. Perhaps that is what is causing your particular problem. In such cases it appears that the fix is to delete or rename the old "Arduino15" directory and re-install the new IDE.

On Mac OS X:
/Users/(username)/Library/Arduino15 (a.k.a. ~/Library/Arduino15)
(Note: The 'Library' folder is greyed out in Finder. The folder can't be opened with a double-click. To browse the contents of 'Library', ctrl-click on it and select "Open in New Tab" from the pop-up menu.)