Provide a build time default-pager setting

Provide a DEFAULT_PAGER knob so packagers can set the fallback
pager to something appropriate during the build.

Examples:

On (old) solaris systems, /usr/bin/less (typically the first less
found) doesn't understand the default arguments (FXRS), which
forces users to alter their environment (PATH, GIT_PAGER, LESS,
etc) or have a local or global gitconfig before paging works as
expected.

On Debian systems, by policy packages must fall back to the
'pager' command, so that changing the target of the
/usr/bin/pager symlink changes the default pager for all packages
at once.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Ben Walton <bwalton@artsci.utoronto.ca>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/Makefile b/Makefile
index 625866c..18fc50a 100644
--- a/Makefile
+++ b/Makefile
@@ -201,6 +201,10 @@
 #
 # Define NO_REGEX if you have no or inferior regex support in your C library.
 #
+# Define DEFAULT_PAGER to a sensible pager command (defaults to "less") if
+# you want to use something different.  The value will be interpreted by the
+# shell at runtime when it is used.
+#
 # Define DEFAULT_EDITOR to a sensible editor command (defaults to "vi") if you
 # want to use something different.  The value will be interpreted by the shell
 # if necessary when it is used.  Examples:
@@ -1380,6 +1384,13 @@
 BASIC_CFLAGS += -DDEFAULT_EDITOR='$(DEFAULT_EDITOR_CQ_SQ)'
 endif
 
+ifdef DEFAULT_PAGER
+DEFAULT_PAGER_CQ = "$(subst ",\",$(subst \,\\,$(DEFAULT_PAGER)))"
+DEFAULT_PAGER_CQ_SQ = $(subst ','\'',$(DEFAULT_PAGER_CQ))
+
+BASIC_CFLAGS += -DDEFAULT_PAGER='$(DEFAULT_PAGER_CQ_SQ)'
+endif
+
 ALL_CFLAGS += $(BASIC_CFLAGS)
 ALL_LDFLAGS += $(BASIC_LDFLAGS)