Add action to run validation on every commit

Adds some flags to the makefile to make it build on alpine with a
different libc

Makefile

@@ -2,7 +2,7 @@
 
 CC=clang
 LD=clang
-CFLAGS=-Wall -Wextra -Wpedantic -O0 -g3 -std=c23 -fno-omit-frame-pointer -fno-optimize-sibling-calls
+CFLAGS=-Wall -Wextra -Wpedantic -O0 -g3 -std=c23 -fno-omit-frame-pointer -fno-optimize-sibling-calls -D_POSIX_C_SOURCE=200809L
 LDFLAGS?=
 
 SOURCES = $(shell find src/ -type f -name '*.c')