[meson] fix icu-related linking errors in test with amalgam build

test-unicode.c:960: undefined reference to `hb_icu_get_unicode_funcs'
test-unicode.c:961: undefined reference to `hb_icu_get_unicode_funcs'

For now add the icu sources to libharfbuzz also for the amalgam
build, later we need to have a separate harfbuzz-icu module and
link against that, and/or generate harfbuzz.cc.

src/meson.build

@@ -185,11 +185,6 @@ if conf.get('HAVE_GLIB', 0) == 1
   hb_headers += hb_glib_headers
 endif
 
-if conf.get('HAVE_ICU', 0) == 1
-  hb_sources += hb_icu_sources
-  hb_headers += hb_icu_headers
-endif
-
 if conf.get('HAVE_UNISCRIBE', 0) == 1
   hb_sources += ['hb-uniscribe.cc']
   hb_headers += ['hb-uniscribe.h']
@@ -210,6 +205,12 @@ if get_option('amalgam')
   hb_sources = ['harfbuzz.cc']
 endif
 
+# FIXME: move into harfbuzz-icu module
+if conf.get('HAVE_ICU', 0) == 1
+  hb_sources += hb_icu_sources
+  hb_headers += hb_icu_headers
+endif
+
 # harfbuzz
 gen_def = find_program('gen-def.py')
 harfbuzz_def = custom_target('harfbuzz.def',