Drop dependency on GNU sed.

GNU sed supports `-i` (in-place editing) with an optional suffix for the
backup copy.  Non-GNU implementations also support `-i`, but the suffix
is not optional.  Replacing all occurrences of naked `-i` with `-i.bak`
ensures our scripts work equally well with both.

.github/workflows/autotools-cmake.yml

@@ -81,7 +81,6 @@ jobs:
             automake \
             cmake \
             docbook2x \
-            gnu-sed \
             libtool \
             lzip
 
@@ -128,8 +127,14 @@ jobs:
           # Autotools' LT_LIB_M has a hardcoded exclude for "*-*-darwin*" hosts,
           # while macOS does have libm and is successfully found by CMake.
           # We patch the CMake side in line here to get the differ below to empty.
-          export PATH="$(brew --prefix)/opt/gnu-sed/libexec/gnubin:${PATH}"
-          sed 's,-lm,,' -i build_cmake/ROOT/usr/local/lib*/pkgconfig/expat.pc
+          #
+          # Both GNU and BSD sed can edit in-place without creating a backup,
+          # but not with the same syntax.  The syntax for editing in-place
+          # _with_ a backup however is the same, so do that, then remove the
+          # backup so it doesn't show up in the diff later.
+          sed -e 's,-lm,,' -i.bak \
+              build_cmake/ROOT/usr/local/lib*/pkgconfig/expat.pc
+          rm -f build_cmake/ROOT/usr/local/lib*/pkgconfig/expat.pc.bak
         fi
 
         diff \

expat/Makefile.am

@@ -117,7 +117,7 @@ buildlib:
 	@echo 'ERROR:    # find . -name Makefile.am -exec sed \' >&2
 	@echo 'ERROR:          -e "s,libexpat\.la,libexpatw.la," \' >&2
 	@echo 'ERROR:          -e "s,libexpat_la,libexpatw_la," \' >&2
-	@echo 'ERROR:          -i {} +' >&2
+	@echo 'ERROR:          -i.bak {} +' >&2
 	@echo 'ERROR:' >&2
 	@echo 'ERROR:  * Run automake to re-generate Makefile.in files' >&2
 	@echo 'ERROR:' >&2

expat/README.md

@@ -161,7 +161,7 @@ support this mode of compilation (yet):
    `find . -name Makefile.am -exec sed
        -e 's,libexpat\.la,libexpatw.la,'
        -e 's,libexpat_la,libexpatw_la,'
-       -i {} +`
+       -i.bak {} +`
 
 1. Run `automake` to re-write `Makefile.in` files:<br/>
    `automake`

expat/apply-clang-format.sh

@@ -56,5 +56,5 @@ clang-format "${args[@]}" -- "${files[@]}"
 sed \
         -e 's, @$,@,' \
         -e 's,#\( \+\)cmakedefine,#cmakedefine,' \
-        -i \
+        -i.bak \
         expat_config.h.cmake