gprofng: avoid use of non-portable which [PR32166]

Distributions like Debian [0] and Gentoo are phasing out the use of
the non-portable `which` utility. Use POSIX's `command -v` instead.

[0] https://lwn.net/Articles/874049/

gprofng/ChangeLog
	PR gprofng/32166
	* testsuite/lib/Makefile.skel (JAVABIN): Replace use of which.
diff --git a/gprofng/testsuite/lib/Makefile.skel b/gprofng/testsuite/lib/Makefile.skel
index 8ea994d..2c98720 100644
--- a/gprofng/testsuite/lib/Makefile.skel
+++ b/gprofng/testsuite/lib/Makefile.skel
@@ -23,7 +23,7 @@
 SHAREDOPT	= -fpic	-shared
 
 #JAVABIN = /usr/java/latest/bin
-JAVABIN = $(shell dirname `which java`)
+JAVABIN = $(shell dirname `command -v java`)
 JAVA    = $(JAVABIN)/java
 JAVAC   = $(JAVABIN)/javac