Check _XOPEN_SOURCE macro before defining (#2220)
Check _XOPEN_SOURCE macro before defining (#2220)

In jrt.h the _XOPEN_SOURCE macro is defined.
However if the compiler already specifies this as
a default define, it can lead to compiler warnings
or errors.

By adding a macro check the warnings/errors can be
avoided.

JerryScript-DCO-1.0-Signed-off-by: Peter Gal pgal.u-szeged@partner.samsung.com
akosthekiss/jerryscript,yichoi/jerryscript,grgustaf/jerryscript,LaszloLango/jerryscript,bzsolt/jerryscript,bsdelf/jerryscript,dbatyai/jerryscript,zherczeg/jerryscript,bzsolt/jerryscript,bsdelf/jerryscript,dbatyai/jerryscript,jerryscript-project/jerryscript,akosthekiss/jerryscript,bsdelf/jerryscript,dbatyai/jerryscript,LaszloLango/jerryscript,jerryscript-project/jerryscript,zherczeg/jerryscript,yichoi/jerryscript,bsdelf/jerryscript,zherczeg/jerryscript,akosthekiss/jerryscript,zherczeg/jerryscript,LaszloLango/jerryscript,bsdelf/jerryscript,yichoi/jerryscript,grgustaf/jerryscript,robertsipka/jerryscript,jerryscript-project/jerryscript,grgustaf/jerryscript,robertsipka/jerryscript,grgustaf/jerryscript,gabrielschulhof/jerryscript,dbatyai/jerryscript,LaszloLango/jerryscript,zherczeg/jerryscript,yichoi/jerryscript,robertsipka/jerryscript,gabrielschulhof/jerryscript,robertsipka/jerryscript,bzsolt/jerryscript,gabrielschulhof/jerryscript,gabrielschulhof/jerryscript,akosthekiss/jerryscript,grgustaf/jerryscript,yichoi/jerryscript,robertsipka/jerryscript,LaszloLango/jerryscript,jerryscript-project/jerryscript,bsdelf/jerryscript,bzsolt/jerryscript,jerryscript-project/jerryscript,robertsipka/jerryscript,grgustaf/jerryscript,akosthekiss/jerryscript,dbatyai/jerryscript,bzsolt/jerryscript,gabrielschulhof/jerryscript