Make patches relative to where tarballs are extracted

Ever since an old patch version, it has (for reasonable security
reasons) not supported patched with ../ in the filename.
Many of our patches have been relying on this behaviour being OK,
because we start off with an ancient patch version that didn't perform
such checks. As soon as we need this behaviour after we build a newer
patch though, we will have problems.

So, let's change the policy.
Patches are relative to where tarballs are extracted, rather than the
"working directory" - e.g. have patches for `coreutils-9.4/src/cp.c`
instead of `src/cp.c`.
Keeping this consistent has a few implications;
- patches are applied from the build/ directory in bash era now, with
  `-p0`
- when patches are manually applied in the bash era, use `-p` as
  required, usually `-p1`
- in kaem era where patches are always manually applied, `-p1` is used

steps/binutils-2.41/patches/new-gettext.patch

@@ -4,8 +4,8 @@ SPDX-License-Identifier: GPL-3.0-or-later
 
 In new gettext external is required for AM_GNU_GETTEXT.
 
---- intl/configure.ac	2023-02-07 18:57:56.350832016 +1100
-+++ intl/configure.ac	2023-02-07 18:58:07.310054484 +1100
+--- binutils-2.41/intl/configure.ac	2023-02-07 18:57:56.350832016 +1100
++++ binutils-2.41/intl/configure.ac	2023-02-07 18:58:07.310054484 +1100
 @@ -4,7 +4,7 @@
  AC_CONFIG_HEADER(config.h)
  AC_CONFIG_MACRO_DIR(../config)

steps/binutils-2.41/patches/no-maint-functions-texi.patch

@@ -4,8 +4,8 @@ SPDX-License-Identifier: GPL-3.0-or-later
 
 Ensure functions.texi dependencies are satisfied.
 
---- libiberty/Makefile.in	2023-12-08 15:18:57.985791235 +1100
-+++ libiberty/Makefile.in	2023-12-08 15:19:15.391252344 +1100
+--- binutils-2.41/libiberty/Makefile.in	2023-12-08 15:18:57.985791235 +1100
++++ binutils-2.41/libiberty/Makefile.in	2023-12-08 15:19:15.391252344 +1100
 @@ -368,12 +368,12 @@
  libiberty.html : $(srcdir)/libiberty.texi $(TEXISRC)
  	$(MAKEINFO) --no-split --html -I$(srcdir) -o $@ $<

steps/binutils-2.41/patches/no-maint-opcodes.patch

@@ -5,8 +5,8 @@ SPDX-License-Identifier: GPL-3.0-or-later
 
 Ensure i386-tbl.h dependencies are satisfied.
 
---- opcodes/Makefile.am	2023-12-08 17:13:05.669136957 +1100
-+++ opcodes/Makefile.am	2023-12-08 17:13:18.410480026 +1100
+--- binutils-2.41/opcodes/Makefile.am	2023-12-08 17:13:05.669136957 +1100
++++ binutils-2.41/opcodes/Makefile.am	2023-12-08 17:13:18.410480026 +1100
 @@ -540,7 +540,7 @@
  # i386-gen will generate all headers in one go.  Use a pattern rule to properly
  # express this, with the inner dash ('-') arbitrarily chosen to be the stem.