Fix C11 detection in the makefile (#7822)
Fix C11 detection in the makefile (#7822)

445a4b6 introudced a makefile script that detects if the toolchain
supports c11, and it looked that it was passing on MacOS and fails on
Ubuntu, looks like Ubuntu's Dash was spawning a background process,
deleted foo.c before gcc tried to compile it.
JackieXie168/redis,JackieXie168/redis,JackieXie168/redis,JackieXie168/redis