macOS: Replace grep -P with perl invocation

macOS has an old grep, which doesn't support option -P and hence Perl-style
regular expressions. One option to solve this is to require macOS users to
install GNU grep with Homebrew and then use ggrep on those systems, however
I've preferred instead to use perl directly, in part because I find that Perl
expression is actually more readable than grep one, even if more verbose.

Signed-off-by: Anton Kolesov <[email protected]>

Author: anthony-kolesov

build-all.sh

@@ -915,12 +915,10 @@ if [ $DO_PDF = --pdf ]; then
     # Texi is a major source of toolchain build errors -- PDF regularly do not
     # work with particular versions of texinfo, but work with others. To
     # workaround those issues build scripts should be aware of texi version.
-    export TEXINFO_VERSION_MAJOR=$(texi2pdf --version | grep -Po '(?<=Texinfo )[0-9]+')
-    # Grep perl look-behind expressions must have a fixed length, so to future
-    # proof for texinfo versions 10+, we have to read variable, because that
-    # wouldn't work: (?<=Texinfo [0-9]+\.)
-    export TEXINFO_VERSION_MINOR=$(texi2pdf --version |
-	grep -Po "(?<=Texinfo $TEXINFO_VERSION_MAJOR\.)[0-9]+")
+    export TEXINFO_VERSION_MAJOR=$(texi2pdf --version | \
+	perl -ne 'print $1 if /Texinfo ([0-9]+)/')
+    export TEXINFO_VERSION_MINOR=$(texi2pdf --version | \
+	perl -ne 'print $2 if /Texinfo ([0-9]+)\.([0-9]+)/')
 
     # There are issues with Texinfo v4 and non-C locales.
     # See http://lists.gnu.org/archive/html/bug-texinfo/2010-03/msg00031.html