fix 2698: cImportPaths doesn't work with dmd and ldc

changelog/fix-cimport-paths.dd

@@ -0,0 +1,3 @@
+Fix issue where cImportPaths wasn't working with dmd and ldc
+
+dub was passing -I<import path> instead of -P-I<import path> as is required by those compilers

source/dub/compilers/dmd.d

@@ -257,7 +257,7 @@
 		}
 
 		if (!(fields & BuildSetting.cImportPaths)) {
-			settings.addDFlags(settings.cImportPaths.map!(s => "-I"~s)().array());
+			settings.addDFlags(settings.cImportPaths.map!(s => "-P-I"~s)().array());
 			settings.cImportPaths = null;
 		}
 

source/dub/compilers/ldc.d

@@ -137,7 +137,7 @@
 		}
 
 		if (!(fields & BuildSetting.cImportPaths)) {
-			settings.addDFlags(settings.cImportPaths.map!(s => "-I"~s)().array());
+			settings.addDFlags(settings.cImportPaths.map!(s => "-P-I"~s)().array());
 			settings.cImportPaths = null;
 		}
 

test/issue2698-cimportpaths-broken-with-dmd-ldc/c_headers/foo.h

@@ -0,0 +1,6 @@
+#include <stdio.h>
+
+int bar(void)
+{
+	printf("func bar in foo.h\n");
+}

test/issue2698-cimportpaths-broken-with-dmd-ldc/dub.sdl

@@ -0,0 +1,5 @@
+name "issue2698-cimportpaths-broken-with-dmd-ldc"
+description "test issue 2698"
+authors "alexander bryan"
+cSourcePaths "source"
+cImportPaths "c_headers"

test/issue2698-cimportpaths-broken-with-dmd-ldc/source/app.d

@@ -0,0 +1,7 @@
+import std.stdio;
+import foo;
+
+void main()
+{
+	bar();
+}

test/issue2698-cimportpaths-broken-with-dmd-ldc/source/foo.c

@@ -0,0 +1 @@
+#include "foo.h"