If an error occurs during an `exec` call, we get empty output

[fpapadopou]

Issue description and reproduction steps

When providing G++ or Clang with parameter files that contain parentheses in their names, PHP's exec function breaks and you get sth like this on the stderr output (caught in command line):

sh: -c: line 0: syntax error near unexpected token `('
sh: -c: line 0: `avr-g++ -Os -ffunction-sections -fdata-sections -fno-exceptions  -I/arduino-core-files-OSX/v105/hardware/tools/avr/lib/gcc/avr/4.3.2/include -I/arduino-core-files-OSX/v105/hardware/tools/avr/lib/gcc/avr/4.3.2/include-fixed -I/arduino-core-files-OSX/v105/hardware/tools/avr/avr/include  -mmcu=atmega328p -DARDUINO=105 -DF_CPU=16000000 -DUSB_VID=null -DUSB_PID=null -MMD  -I/external_cores/override_cores/arduino/ -I/arduino-core-files-OSX/v105/hardware/arduino/cores/arduino -I/arduino-core-files-OSX/v105/hardware/arduino/variants/standard -I/tmp/compiler.elVKPg/libraries/Ethernet(3) -c -o '/tmp/compiler.elVKPg/files/Blink'.o '/tmp/compiler.elVKPg/files/Blink'.cpp 2>&1'
sh: -c: line 0: syntax error near unexpected token `('
sh: -c: line 0: `LD_LIBRARY_PATH=/arduino-core-files-OSX/clang/v3_5/lib:$LD_LIBRARY_PATH /usr/bin/clang --target=msp430 -w -fsyntax-only -fcolor-diagnostics  -I/arduino-core-files-OSX/v105/hardware/tools/avr/lib/gcc/avr/4.3.2/include -I/arduino-core-files-OSX/v105/hardware/tools/avr/lib/gcc/avr/4.3.2/include-fixed -I/arduino-core-files-OSX/v105/hardware/tools/avr/avr/include  -D__AVR_ATmega328P__ -DARDUINO=105 -DF_CPU=16000000  -I/external_cores/override_cores/arduino/ -I/arduino-core-files-OSX/v105/hardware/arduino/cores/arduino -I/arduino-core-files-OSX/v105/hardware/arduino/variants/standard -I/tmp/compiler.elVKPg/libraries/Ethernet(3) -c -o '/tmp/compiler.elVKPg/files/Blink'.o '/tmp/compiler.elVKPg/files/Blink'.cpp 2>&1'

Notice the -I/tmp/compiler.elVKPg/libraries/Ethernet(3) part in both avr-g++ and Clang commands.

As a result, both compilers end up with a syntax error, never executing the requested command.

We do redirect stderr to stdout using 2>&1 in the end of all commands provided to PHP's exec, however this doesn't work for such cases.

Need to find a way to catch this output.