tests: regress: add malformed quoting test

Makefile.am

@@ -80,6 +80,7 @@ EXTRA_DIST =	pkg.m4 \
 		tests/lib1/fragment-quoting-6.pc \
 		tests/lib1/fragment-quoting-7.pc \
 		tests/lib1/malformed-1.pc \
+		tests/lib1/malformed-quoting.pc \
 		tests/lib1/explicit-sysroot.pc \
 		tests/test_env.sh \
 		$(test_scripts) \

tests/lib1/malformed-quoting.pc

@@ -0,0 +1,4 @@
+Name: malformed-quoting
+Version: 1
+Description: None.
+Cflags: '-I/ABC

tests/regress.sh

@@ -27,6 +27,7 @@ tests_init \
 	virtual_variable \
 	fragment_collision \
 	malformed_1 \
+	malformed_quoting \
 	explicit_sysroot
 
 case_sensitivity_body()
@@ -233,6 +234,12 @@ malformed_1_body()
 		pkgconf --validate --with-path="${selfdir}/lib1" malformed-1
 }
 
+malformed_quoting_body()
+{
+	atf_check -s exit:0 -o ignore \
+		pkgconf --validate --with-path="${selfdir}/lib1" malformed-quoting
+}
+
 explicit_sysroot_body()
 {
 	export PKG_CONFIG_SYSROOT_DIR=/sysroot