Install everything in PREFIX, set EXTRA_PATH to find it there.

--- ./Makefile.in~	2016-02-06 01:29:16.595090365 +0100
+++ ./Makefile.in	2016-02-06 09:29:04.286008931 +0100
@@ -133,9 +133,9 @@
 # require for testing here (like TCLX_LIBRARY).
 #========================================================================

-EXTRA_PATH	= $(top_builddir):$(TCL_BIN_DIR)
+EXTRA_PATH	= $(top_builddir):$(TCL_BIN_DIR):$(libdir)
 #EXTRA_PATH     = $(top_builddir):$(TCL_BIN_DIR):$(TK_BIN_DIR)
-TCLLIBPATH      = $(top_builddir)
+TCLLIBPATH      = $(pkglibdir)
 TCLSH_ENV	= TCL_LIBRARY=`@CYGPATH@ $(TCL_SRC_DIR)/library` \
 		  @LD_LIBRARY_PATH_VAR@="$(EXTRA_PATH):$(@LD_LIBRARY_PATH_VAR@)" \
 		  PATH="$(EXTRA_PATH):$(PATH)" \
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<tr><td><span title='2021-05-22 17:08:13 +0200'>2021-05-22</span></td><td><a href='/guix/commit/gnu/packages/ninja.scm?id=bd6cb1d4ebb3da1110025e1a73a299bed4174035'>gnu: ninja: Update to 1.10.2.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/ninja.scm (ninja): Update to 1.10.2.
[arguments]: Remove trailing #t's.
</span></span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2020-02-03 15:29:15 +0100'>2020-02-03</span></td><td><a href='/guix/commit/gnu/packages/ninja.scm?id=8928425756a9cc162bc38888a7c7084fcc777bd1'>gnu: ninja: Update to 1.10.0.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/ninja.scm (ninja): Update to 1.10.0.
</span></span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2020-02-03 15:29:15 +0100'>2020-02-03</span></td><td><a href='/guix/commit/gnu/packages/ninja.scm?id=181171ffdb4bdb534a4ce0fb631fa7cf103a2996'>gnu: ninja: Do not use unstable tarball.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/ninja.scm (ninja)[source]: Change to GIT-FETCH.
</span></span></td><td>Marius Bakke</td></tr>