This version ships the following patches on top of upstream GNU m4 1.4.20:
windows-binary-mode.patch -- At the start of output_init() in src/output.c, call SET_BINARY(STDOUT_FILENO) when SET_BINARY is defined. On Windows, the C runtime defaults text mode on stdout, which translates newlines to CRLF. m4 must write its output in binary mode so generated files are not corrupted; this matches the usual MinGW/MSVC pattern for binary-safe stdout.
stdint-comment-subst.patch -- In lib/stdint.in.h, the comment that mentions the autoconf token @NEXT_STDINT_H@ is rewritten so the @...@ sequence is split with spaces (@ NEXT_STDINT_H @). That keeps the comment readable but avoids accidental processing of the token as a substitution placeholder by tooling that scans for @NAME@ patterns during the Bazel build.
musl-libc-compat.patch -- Replaces #error directives in gnulib's fpending.c and freadahead.c with safe return 1 fallbacks, allowing m4 to compile on platforms with opaque FILE structs (e.g. musl libc) where these files would otherwise fail to build. This mirrors the approach taken by rules_m4 (see jmillikin/rules_m4@275873f), which stubs out these functions because musl provides __fpending and __freadahead natively and these gnulib replacements should not be compiled in the first place.
error-h-shadowing.patch -- Renames all #include <error.h> to #include <m4-error.h> across 14 source files in lib/ and src/. On glibc-based systems (e.g. NixOS), a system-level error.h with include guard _ERROR_H can shadow gnulib's generated error.h (guard _GL_ERROR_H) when both are on -isystem paths. The corresponding GENERATED_SRCS entry in BUILD.bazel maps lib/m4-error.h to the lib/error.in.h template, so there is no filename collision. The gnulib template still chains to the system error.h via #include_next on GCC/Clang. This addresses the same issue described in jmillikin/rules_m4#23.