Makefile: add/remove comments at top and tweak whitespace

The top of the Makfile is mostly separated into logical steps like set
default configuration, set programs etc., but there's some deviation
from that.

Let's add mostly comments where they're missing, remove those that
don't add anything. The whitespace tweaking makes subsequent patches
smaller.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -507,15 +507,14 @@ GIT-VERSION-FILE: FORCE
 -include GIT-VERSION-FILE
 
 # CFLAGS and LDFLAGS are for the users to override from the command line.
-
 CFLAGS = -g -O2 -Wall
 LDFLAGS =
 ALL_CFLAGS = $(CPPFLAGS) $(CFLAGS)
 ALL_LDFLAGS = $(LDFLAGS)
-
-# Create as necessary, replace existing, make ranlib unneeded.
 ARFLAGS = rcs
 
+# Set our default configuration.
+#
 # Among the variables below, these:
 #   gitexecdir
 #   template_dir
@@ -560,6 +559,7 @@ perllibdir_relative = $(patsubst $(prefix)/%,%,$(perllibdir))
 
 export prefix bindir sharedir sysconfdir gitwebdir perllibdir localedir
 
+# Set our default programs
 CC = cc
 AR = ar
 RM = rm -f
@@ -587,10 +587,6 @@ SP_EXTRA_FLAGS =
 
 SPATCH_FLAGS = --all-includes --patch .
 
-
-
-### --- END CONFIGURATION SECTION ---
-
 BASIC_CFLAGS = -I.
 BASIC_LDFLAGS =