build: wire new src dirs, crt objects, and make check into Autotools

configure.ac

@@ -26,6 +26,9 @@ AM_INIT_AUTOMAKE([foreign subdir-objects])
 # (including clang), so it cannot be used to enforce the single-compiler rule.
 # Verify the compiler is genuinely GCC, not a compatible one.
 AC_PROG_CC
+# AM_PROG_AS: library sources include raw x86_64 assembly (the setjmp family
+# in src/setjmp/x86_64/*.s), which automake compiles through CCAS/CCASFLAGS.
+AM_PROG_AS
 AC_MSG_CHECKING([whether the compiler is GCC])
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [
 #if !defined(__GNUC__) || defined(__clang__)
@@ -58,7 +61,16 @@ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [])],
                    AC_MSG_ERROR([$CC does not support -std=$vlibc_cstd])])
 CFLAGS=$vlibc_save_CFLAGS
 
-AC_SUBST([VLIBC_CFLAGS], ["-std=$vlibc_cstd -Wall -Wextra"])
+# -fno-stack-protector: distro GCC builds enable -fstack-protector-strong by
+# default, which would make library objects reference __stack_chk_fail — a
+# symbol vlibc does not provide yet. Every make-check test binary and every
+# -nostdlib -static consumer links against the plain archive, and one
+# undefined __stack_chk_fail in it breaks the whole self-hosting link. A
+# bootstrap libc must build its own objects without the protector (the stack
+# protector runtime lands with the hardening work, after which this flag is
+# revisited). Tests compile with the same flag (tests/Makefile.am wiring in
+# Makefile.am).
+AC_SUBST([VLIBC_CFLAGS], ["-std=$vlibc_cstd -Wall -Wextra -fno-stack-protector"])
 
 # ---- Compatibility profile ----------------------------------------------
 # Exactly one of the five profiles is active. They are mutually exclusive;