[gcc r16-5873] libgomp: Fix offload_target with additional sources

[Andrew Stubbs]

https://gcc.gnu.org/g:1eb2aeed08ca8732e5146974bcf5512bdfcd2e5f

commit r16-5873-g1eb2aeed08ca8732e5146974bcf5512bdfcd2e5f
Author: Andrew Stubbs <ams@baylibre.com>
Date:   Wed Dec 3 14:34:59 2025 +0000

    libgomp: Fix offload_target with additional sources
    
    The offload_target_* effective target checks called libgomp_target_compile in a
    way that altered global state if additional sources were configured.
    
    This patch ignores additional sources if the compile check uses no sources (a
    compiler probe, only), thus fixing the problem.
    
    libgomp/ChangeLog:
    
            * testsuite/lib/libgomp.exp (libgomp_target_compile): Don't use
            additional sources if there are no primary sources.

Diff:
---
 libgomp/testsuite/lib/libgomp.exp | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/libgomp/testsuite/lib/libgomp.exp b/libgomp/testsuite/lib/libgomp.exp
index f5683b50725a..2fc811d91c64 100644
--- a/libgomp/testsuite/lib/libgomp.exp
+++ b/libgomp/testsuite/lib/libgomp.exp
@@ -295,7 +295,9 @@ proc libgomp_target_compile { source dest type options } {
 	set options [concat "$ALWAYS_CFLAGS" $options]
     }
 
-    set options [dg-additional-files-options $options $source $dest $type]
+    if { $source != "" } {
+        set options [dg-additional-files-options $options $source $dest $type]
+    }
 
     set result [target_compile $source $dest $type $options]