Test stripping of duplicate flags

pkg-config aggressively strips all duplicate arguments from the final
output it builds. This is not only and optimization, but it also allows
the flag ordering to work correctly when a package on the command line
is required by another on the command line.

check/Makefile.am

@@ -15,6 +15,7 @@ TESTS = \
 	check-missing \
 	check-idirafter \
 	check-sort-order \
+	check-duplicate-flags \
 	check-whitespace \
 	check-cmd-options \
 	check-version \
@@ -61,4 +62,6 @@ EXTRA_DIST = \
 	sort/sort/sort-order-3-2.pc \
 	sort-order-1-3.pc \
 	sort/sort-order-2-3.pc \
-	sort/sort/sort-order-3-3.pc
+	sort/sort/sort-order-3-3.pc \
+	flag-dup-1.pc \
+	flag-dup-2.pc

check/check-duplicate-flags

@@ -0,0 +1,15 @@
+#! /bin/sh
+
+set -e
+
+. ${srcdir}/common
+
+RESULT="-DPATH2 -DFOO -DPATH1 -I/path/include"
+run_test --cflags flag-dup-1 flag-dup-2
+RESULT="-DPATH1 -DFOO -DPATH2 -I/path/include"
+run_test --cflags flag-dup-2 flag-dup-1
+
+RESULT="-Wl,--whole-archive --Wl,--no-whole-archive -Xlinker -R /path/lib \
+-L/path/lib -lpath2 -lpath1 -lm"
+run_test --libs flag-dup-1 flag-dup-2
+run_test --libs flag-dup-2 flag-dup-1

check/flag-dup-1.pc

@@ -0,0 +1,10 @@
+prefix=/path
+exec_prefix=${prefix}
+libdir="${exec_prefix}/lib"
+includedir="${prefix}/include"
+
+Name: Flag duplicate test 1
+Description: Test package for checking stripping of duplicate flags
+Version: 1.0.0
+Libs: -L${libdir} -lpath1 -Wl,--whole-archive -lm --Wl,--no-whole-archive -Xlinker -R -Xlinker ${libdir}
+Cflags: -I${includedir} -DPATH1 -DFOO

check/flag-dup-2.pc

@@ -0,0 +1,11 @@
+prefix=/path
+exec_prefix=${prefix}
+libdir="${exec_prefix}/lib"
+includedir="${prefix}/include"
+
+Name: Flag duplicate test 2
+Description: Test package for checking stripping of duplicate flags
+Version: 1.0.0
+Libs: -L${libdir} -lpath2 -Wl,--whole-archive -lm --Wl,--no-whole-archive -Xlinker -R -Xlinker ${libdir}
+Cflags: -I${includedir} -DPATH2 -DFOO
+Requires: flag-dup-1