guix: patch /gnu/store paths out of winpthreads

At the same time, align the docs for all patches that do the same thing.

contrib/guix/manifest.scm

@@ -128,13 +128,17 @@ desirable for building Bitcoin Core release binaries."
   (package-with-extra-patches binutils
     (search-our-patches "binutils-unaligned-default.patch")))
 
+(define (winpthreads-patches mingw-w64-x86_64-winpthreads)
+  (package-with-extra-patches mingw-w64-x86_64-winpthreads
+    (search-our-patches "winpthreads-remap-guix-store.patch")))
+
 (define (make-mingw-pthreads-cross-toolchain target)
   "Create a cross-compilation toolchain package for TARGET"
   (let* ((xbinutils (binutils-mingw-patches (cross-binutils target)))
          (machine (substring target 0 (string-index target #\-)))
-         (pthreads-xlibc (make-mingw-w64 machine
+         (pthreads-xlibc (winpthreads-patches (make-mingw-w64 machine
                                          #:xgcc (cross-gcc target #:xgcc (gcc-mingw-patches base-gcc))
-                                         #:with-winpthreads? #t))
+                                         #:with-winpthreads? #t)))
          (pthreads-xgcc (cross-gcc target
                                     #:xgcc (gcc-mingw-patches mingw-w64-base-gcc)
                                     #:xbinutils xbinutils

contrib/guix/patches/gcc-remap-guix-store.patch

@@ -1,14 +1,9 @@
-From aad25427e74f387412e8bc9a9d7bbc6c496c792f Mon Sep 17 00:00:00 2001
+Without ffile-prefix-map, the debug symbols will contain paths for the
-From: Andrew Chow <achow101-github@achow101.com>
+guix store which will include the hashes of each package. However, the
-Date: Wed, 6 Jul 2022 16:49:41 -0400
+hash for the same package will differ when on different architectures.
-Subject: [PATCH] guix: remap guix store paths to /usr
+In order to be reproducible regardless of the architecture used to build
+the package, map all guix store prefixes to something fixed, e.g. /usr.
 
----
- libgcc/Makefile.in | 2 +-
- 1 file changed, 1 insertion(+), 1 deletion(-)
-
-diff --git a/libgcc/Makefile.in b/libgcc/Makefile.in
-index 851e7657d07..476c2becd1c 100644
 --- a/libgcc/Makefile.in
 +++ b/libgcc/Makefile.in
 @@ -854,7 +854,7 @@ endif

contrib/guix/patches/winpthreads-remap-guix-store.patch

@@ -0,0 +1,17 @@
+Without ffile-prefix-map, the debug symbols will contain paths for the
+guix store which will include the hashes of each package. However, the
+hash for the same package will differ when on different architectures.
+In order to be reproducible regardless of the architecture used to build
+the package, map all guix store prefixes to something fixed, e.g. /usr.
+
+--- a/mingw-w64-libraries/winpthreads/Makefile.in
++++ b/mingw-w64-libraries/winpthreads/Makefile.in
+@@ -478,7 +478,7 @@ top_build_prefix = @top_build_prefix@
+ top_builddir = @top_builddir@
+ top_srcdir = @top_srcdir@
+ SUBDIRS = . tests
+-AM_CFLAGS = -Wall -DWIN32_LEAN_AND_MEAN $(am__append_1)
++AM_CFLAGS = -Wall -DWIN32_LEAN_AND_MEAN $(am__append_1) $(shell find /gnu/store -maxdepth 1 -mindepth 1 -type d -exec echo -n " -ffile-prefix-map={}=/usr" \;)
+ ACLOCAL_AMFLAGS = -I m4
+ lib_LTLIBRARIES = libwinpthread.la
+ include_HEADERS = include/pthread.h include/sched.h include/semaphore.h include/pthread_unistd.h include/pthread_time.h include/pthread_compat.h include/pthread_signal.h