p5-text-bibtex: remove blacklisting and add -std=c99 to compile flags

This is a better build fix for 10.6 and earlier.  In particular, gcc-4.2
does, in fact, support C99 but not by default as newer compilers do.

Thanks to @ryandesign and @jmroot for clarifying the issue.

perl/p5-text-bibtex/Portfile

@@ -1,11 +1,11 @@
 # -*- coding: utf-8; mode: tcl; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- vim:fenc=utf-8:ft=tcl:et:sw=4:ts=4:sts=4
 
 PortSystem          1.0
-PortGroup           compiler_blacklist_versions 1.0
 PortGroup           perl5 1.0
 
 perl5.branches      5.26 5.28
 perl5.setup         Text-BibTeX 0.86
+revision            1
 platforms           darwin
 maintainers         nomaintainer
 license             {Artistic-1 GPL}
@@ -29,17 +29,19 @@ if {${perl5.major} != ""} {
     depends_lib-append \
                     port:p${perl5.major}-unicode-normalize
 
-    # blacklist compilers that don't support C99
-    # btparse/tests/namebug.c:193: error: ‘for’ loop initial declaration used outside C99 mode
-    compiler.blacklist  *gcc-3.* *gcc-4.* {clang < 300}
-
-    perl5.use_module_build
-
     # in inc/MyBuilder.pm, copy_if_modified is called on binaries and libraries
     # the libraries and binaries are then modified (install names changed)
     # copy_if_modified, however, sets all files as read only
     #    see https://metacpan.org/pod/release/LEONT/Module-Build-0.4220/lib/Module/Build/API.pod#copy_if_modified
     #    see https://github.com/Perl-Toolchain-Gang/Module-Build/blob/master/lib/Module/Build/Base.pm#L5600
     # patch temporarily makes the files writable before changing them
-    patchfiles-append patch-permissions.diff
+    patchfiles-append \
+                    patch-permissions.diff \
+
+    # add -std=c99 to compile flags to fix build for default compilers on 10.6 and earlier
+    # btparse/tests/namebug.c:193: error: ‘for’ loop initial declaration used outside C99 mode
+    patchfiles-append \
+                    patch-extra-flags.diff
+
+    perl5.use_module_build
 }

perl/p5-text-bibtex/files/patch-extra-flags.diff

@@ -0,0 +1,11 @@
+--- inc/MyBuilder.pm.orig	2019-04-03 15:32:39.000000000 -0700
++++ inc/MyBuilder.pm	2019-04-03 15:36:49.000000000 -0700
+@@ -17,7 +17,7 @@
+ use File::Path qw.mkpath.;
+ use Cwd 'abs_path';
+
+-my @EXTRA_FLAGS = ();
++my @EXTRA_FLAGS = ("-std=c99");
+ my @BINARIES = qw(biblex bibparse dumpnames);
+
+ ## debug