Document AWESOME_CFLAGS, and use only with gcc

awesome's default compiler flags work only with gcc, so we only use
them if gcc is detected.

Additionally, you can now avoid using these default flags by adding
AWESOME_CFLAGS="" to your make command lines.

Makefile.am

@@ -32,11 +32,15 @@ defconfig.h: $(srcdir)/awesomerc
 	@$(SED) 's,\\,\\\\,g;s/$$/ \\/;s/"/\\"/g' "$(srcdir)/awesomerc" >> defconfig.h
 	@echo "\"" >> defconfig.h
 
+if USING_GCC
+# If you are using gcc, and want to deactivate this default set of
+# compile flags, run make with AWESOME_CFLAGS="".
 AWESOME_CFLAGS = -std=gnu99 -ggdb3 -pipe \
 		 -Wall -Wextra \
 		 -Wundef -Wshadow -Wcast-align -Wwrite-strings -Wsign-compare \
 		 -Wunused -Winit-self -Wpointer-arith -Wredundant-decls \
 		 -Wmissing-prototypes -Wmissing-format-attribute -Wmissing-noreturn
+endif
 AM_CPPFLAGS = $(XFT_CFLAGS) $(X_CFLAGS) $(CAIRO_CFLAGS) $(CONFUSE_CFLAGS) $(XRANDR_CFLAGS) $(XINERAMA_CFLAGS) $(AWESOME_CFLAGS)
 
 bin_PROGRAMS += awesome

README

@@ -24,6 +24,9 @@ proper parameters, and build and install:
   make
   make install # might need root permissions
 
+If you're using gcc as your compiler and do not want awesome's default set
+of warning flags, add AWESOME_CFLAGS="" to your "make" lines.
+
 Running awesome
 -----------
 Add the following line to your .xinitrc to start awesome using startx

configure.ac

@@ -41,6 +41,8 @@ AM_CONDITIONAL([HAVE_ASCIIDOC], [test "x$ASCIIDOC" != "x:"])
 AM_CONDITIONAL([HAVE_XMLTO],    [test "x$XMLTO"    != "x:"])
 AM_CONDITIONAL([HAVE_DOXYGEN],  [test "x$DOXYGEN"  != "x:"])
 
+AM_CONDITIONAL([USING_GCC], [test "x$GCC" = "xyes"])
+
 # Checks for libraries.
 AC_PATH_XTRA
 PKG_CHECK_MODULES([CAIRO], [cairo],,