[glibc] Makefile: Do not install the container testroot if not running tests

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=b6804fb36e67b2c8e37d48cc106313cfa34bbf19

commit b6804fb36e67b2c8e37d48cc106313cfa34bbf19
Author: Adhemerval Zanella <[email protected]>
Date:   Wed Jun 10 18:25:56 2026 -0300

    Makefile: Do not install the container testroot if not running tests
    
    Every subdirectory tests target depends on
    $(objpfx)testroot.pristine/install.stamp, whose recipe performs a full
    DESTDIR installation (about 12s and 154MB on x86_64).  The testroot is
    only consumed by the container tests, which do not run when
    run-built-tests is no, so skip it entirely in that case.
    
    This saves about 10s on x86_64 [1] and 30s on aarch64 [2].
    
    [1] Ryzen 5900x, 12c/24t, gcc 16.1.1, binutils 2.26, and GNU make 4.3
    [2] N1, 80c, gcc 15.1.1, binutils 2.25, GNU make 4.3
    
    Reviewed-by: Sam James <[email protected]>

Diff:
---
 Makefile | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/Makefile b/Makefile
index 7d46e8387d..23f3c1895d 100644
--- a/Makefile
+++ b/Makefile
@@ -792,8 +792,13 @@ else
 LINKS_DSO_PROGRAM = links-dso-program
 endif
 
+# The testroot is only used by the container tests, which are not run
+# when run-built-tests is no; skip the installation entirely in that
+# case.
+ifeq ($(run-built-tests),yes)
 $(tests-container) $(addsuffix /tests,$(subdirs)) : \
 		$(objpfx)testroot.pristine/install.stamp
+endif
 $(objpfx)testroot.pristine/install.stamp :
 	test -d $(objpfx)testroot.pristine || \
 	  mkdir $(objpfx)testroot.pristine