qmake: Use pkgconfig feature

Instead of using r2 to get the lib and include paths use the builtin
qmake feature for pkgconfig. Still needs a tweak to work with
sys/user.sh installations.

src/lib_radare2.pri

@@ -8,27 +8,8 @@ win32 {
     } else {
         LIBS += -L"$$PWD/../iaito_win32/radare2/lib64"
     }
-} else {
-    # check if r2 is available
-    system(r2 > /dev/null 2>&1) {
 
-        # see https://github.com/hteso/iaito/pull/5#issuecomment-290433796
-        RADARE2_INCLUDE_PATH = $$system(r2 -H | grep INCDIR | sed 's/[^=]*=//')
-        RADARE2_LIB_PATH = $$system(r2 -H | grep LIBDIR | sed 's/[^=]*=//')
-
-        !isEmpty(RADARE2_INCLUDE_PATH) {
-            INCLUDEPATH *= $$RADARE2_INCLUDE_PATH
-            LIBS *= -L$$RADARE2_LIB_PATH
-        } else {
-            error("sorry could not find radare2 lib")
-        }
-    } else {
-        error("r2 not found/in path")
-    }
-}
-
-
-LIBS += \
+    LIBS += \
         -lr_core \
         -lr_config \
         -lr_cons \
@@ -52,4 +33,14 @@ LIBS += \
         -lr_fs \
         -lr_magic \
         -lr_crypto
+} else {
+    R2_USER_PKGCONFIG = $$(HOME)/bin/prefix/radare2/lib/pkgconfig
+    exists($$R2_USER_PKGCONFIG) {
+        # caution: may not work for cross compilations
+        QMAKE_PKG_CONFIG = PKG_CONFIG_PATH=$$R2_USER_PKGCONFIG pkg-config
+    }
+
+    CONFIG += link_pkgconfig
+    PKGCONFIG += r_core
+}