fix i18n compilation on brew/MacOS

When using brew, <libintl.h> and the associated library are installed
under /opt/brew/{include,lib}.  Our configure script did not check
these locations, the files were not found and thus i18n was
unavailable and disabled.

I've added the internal variables EXTRA_INCLUDEDIRS_TO_CHECK and
EXTRA_LIBDIRS_TO_CHECK to the configure script.  They expand the
directories checked by check_include() and find_lib() and can be set
depending on the build environment so we don't need to check these
directories on every non-brew/MacOS build.

We also need to use the extra include directories when building our
test targets: util.test includes "common.h" which in turn includes
<libintl.h> which needs extra flags as described above.
Because using all $GBSCFLAGS messes up our test build, we filter
only for the -I include paths.

HISTORY

@@ -2,14 +2,16 @@
 gbsplay HISTORY
 
 
-2024/04/17  -  unreleased
+2024/xx/xx  -  unreleased
 ~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Bugfixes:
 
 - gbsplay
   - don't mess up the screen with underrun errors from the ALSA plugout
     when resuming from a pause
+- build process:
+  - fix i18n on brew/MaOS
 
 Enhancements:
 

Makefile

@@ -592,7 +592,7 @@ config.mk: configure
 
 %.test: %.c
 	@echo TEST $<
-	$(Q)$(HOSTCC) -DENABLE_TEST=1 -o $@$(binsuffix) $< -lm
+	$(Q)$(HOSTCC) $(filter -I%,$(GBSCFLAGS)) -DENABLE_TEST=1 -o $@$(binsuffix) $< -lm
 	$(Q)./$@$(binsuffix)
 	$(Q)rm ./$@$(binsuffix)
 

configure

@@ -52,6 +52,9 @@ hostalias=
 windows_build=
 windows_libprefix=
 
+EXTRA_INCLUDEDIRS_TO_CHECK=
+EXTRA_LIBDIRS_TO_CHECK=
+
 ## define sane environment
 unset LC_ALL LC_CTYPE LC_NUMERIC LC_TIME LC_COLLATE LC_MONETARY \
       LC_MESSAGES LC_PAPER LC_NAME LC_ADDRESS LC_TELEPHONE      \
@@ -84,7 +87,7 @@ die()
 check_include()
 {
     local include="$1"
-    local includedirs="${2-} /usr/local/include /opt/local/include"
+    local includedirs="${2-} /usr/local/include /opt/local/include ${EXTRA_INCLUDEDIRS_TO_CHECK}"
     local extraline="${3-}"
     local includename="$(echo "$include" | sed -e 's@[/\.-]@_@g')"
     eval "value=\${have_${includename}-}"
@@ -115,7 +118,7 @@ find_lib()
     local INFILE="$TEMPDIR/fl.c"
     local lib="$1"
     local libname="$(echo "$lib" | sed -e 's@[/\.-]@_@g')"
-    local libdirs="${2-} /usr/local/lib /opt/local/lib"
+    local libdirs="${2-} /usr/local/lib /opt/local/lib ${EXTRA_LIBDIRS_TO_CHECK}"
 
     cat > "$INFILE"
 
@@ -622,6 +625,8 @@ case "$BUILDOS" in
     Darwin)
         setdefault build_test yes
         append_nodupe CFLAGS "-D_DARWIN_C_SOURCE=1"
+        EXTRA_INCLUDEDIRS_TO_CHECK=/opt/homebrew/include
+        EXTRA_LIBDIRS_TO_CHECK=/opt/homebrew/lib
         ;;
 
     MSYS_*)