Build systems and configuration scripts must respect standard environment variables and provide proper override mechanisms. This ensures flexibility for users with different build environments, cross-compilation needs, and custom toolchain requirements. Always use the `?=` operator in Makefiles to set defaults while allowing environment overrides, and use `override +=` to append mandatory flags: ```make # Allow environment override with sensible defaults CFLAGS ?= -O3 -Wall -Wextra CC ?= clang # Append mandatory flags that cannot be overridden override CFLAGS += -std=gnu11 -fPIC -Ilib/include ``` For configuration detection, provide compiler flag overrides as escape hatches: ```c // Allow compile-time override while providing automatic detection #if !defined(TS_BIG_ENDIAN) #if (defined(__BYTE_ORDER__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__) #define TS_BIG_ENDIAN 1 #else #define TS_BIG_ENDIAN 0 #endif #endif ``` Never hardcode or remove the ability to override critical build variables like CC, CFLAGS, CXXFLAGS, or LDFLAGS. Users may need to specify custom compilers, cross-compilation toolchains, or additional flags for their specific build environments. This principle applies to all build systems including Makefiles, CMake, and custom build scripts.