[PATCH] testsuite/C++: suppress filename canonicalization in module tests

[Jan Beulich <jbeulich@suse.com>]

The pathname underneath gcm.cache/ is determined from the effective name
used for the main input file of a particular module. When modules are
built, no canonicalization occurs for the main input file. Hence the
module file wouldn't be found if a different (the canonicalized) file
name was used when importing that same module. (This is an effect of
importing happening in the preprocessor, just like #include handling.)

Since it doesn't look easy to make module generation use libcpp's
maybe_shorter_path() (in fact I'd consider this a layering violation,
while cloning the logic would - at least in principle - be prone to both
going out of sync), simply suppress system header path canonicalization
for the respective tests.

gcc/testsuite/

	* g++.dg/modules/alias-1_b.C: Add -fno-canonical-system-headers.
	* g++.dg/modules/alias-1_d.C: Likewise.
	* g++.dg/modules/alias-1_e.C: Likewise.
	* g++.dg/modules/alias-1_f.C: Likewise.
	* g++.dg/modules/cpp-6_c.C: Likewise.
	* g++.dg/modules/dir-only-2_b.C: Likewise.
---
Strictly speaking it could be necessary to also suppress
canonicalization when generating the modules, but for now they're self-
contained, i.e. don't include any "real" system headers. IOW at the
moment the tests aren't susceptible to the issue at generation time.

--- a/gcc/testsuite/g++.dg/modules/alias-1_b.C
+++ b/gcc/testsuite/g++.dg/modules/alias-1_b.C
@@ -1,4 +1,4 @@
-// { dg-additional-options "-fmodules-ts -fdump-lang-module -isystem [srcdir]" }
+// { dg-additional-options "-fmodules-ts -fdump-lang-module -isystem [srcdir] -fno-canonical-system-headers" }
 
 // Alias at the header file.  We have one CMI file
 import "alias-1_a.H";
--- a/gcc/testsuite/g++.dg/modules/alias-1_d.C
+++ b/gcc/testsuite/g++.dg/modules/alias-1_d.C
@@ -1,4 +1,4 @@
-// { dg-additional-options "-fmodules-ts -isystem [srcdir]" }
+// { dg-additional-options "-fmodules-ts -isystem [srcdir] -fno-canonical-system-headers" }
 // { dg-module-cmi kevin }
 
 export module kevin;
--- a/gcc/testsuite/g++.dg/modules/alias-1_e.C
+++ b/gcc/testsuite/g++.dg/modules/alias-1_e.C
@@ -1,4 +1,4 @@
-// { dg-additional-options "-fmodules-ts -isystem [srcdir]" }
+// { dg-additional-options "-fmodules-ts -isystem [srcdir] -fno-canonical-system-headers" }
 
 import bob;
 import kevin;
--- a/gcc/testsuite/g++.dg/modules/alias-1_f.C
+++ b/gcc/testsuite/g++.dg/modules/alias-1_f.C
@@ -1,4 +1,4 @@
-// { dg-additional-options "-fmodules-ts -fdump-lang-module -isystem [srcdir]" }
+// { dg-additional-options "-fmodules-ts -fdump-lang-module -isystem [srcdir] -fno-canonical-system-headers" }
 
 import kevin;
 import bob;
--- a/gcc/testsuite/g++.dg/modules/cpp-6_c.C
+++ b/gcc/testsuite/g++.dg/modules/cpp-6_c.C
@@ -1,5 +1,5 @@
 // { dg-do preprocess }
-// { dg-additional-options "-fmodules-ts -isystem [srcdir]" }
+// { dg-additional-options "-fmodules-ts -isystem [srcdir] -fno-canonical-system-headers" }
 
 #define empty
 #define nop(X) X
--- a/gcc/testsuite/g++.dg/modules/dir-only-2_b.C
+++ b/gcc/testsuite/g++.dg/modules/dir-only-2_b.C
@@ -1,5 +1,5 @@
 // { dg-do preprocess }
-// { dg-additional-options "-fmodules-ts -fdirectives-only -isystem [srcdir]" }
+// { dg-additional-options "-fmodules-ts -fdirectives-only -isystem [srcdir] -fno-canonical-system-headers" }
 // a comment
 module; // line
 frob