Add a build config for bootstrapping at -Og

Although BOOT_CFLAGS can be used to bootstrap with -Og, having a
dedicated build config is sometimes more convenient.

2019-07-08  Richard Sandiford  <richard.sandiford@arm.com>

config/
	* bootstrap-Og.mk: New file.

gcc/
	* doc/install.texi (bootstrap-Og): Document.

From-SVN: r273193

config/ChangeLog

+2019-07-08  Richard Sandiford  <richard.sandiford@arm.com>
+
+	* bootstrap-Og.mk: New file.
+
 2019-06-25  Kwok Cheung Yeung  <kcy@codesourcery.com>
             Andrew Stubbs  <ams@codesourcery.com>
 

config/bootstrap-Og.mk

+BOOT_CFLAGS := -Og $(filter-out -O%, $(BOOT_CFLAGS))

gcc/ChangeLog

 2019-07-08  Richard Sandiford  <richard.sandiford@arm.com>
 
+	* doc/install.texi (bootstrap-Og): Document.
+
+2019-07-08  Richard Sandiford  <richard.sandiford@arm.com>
+
 	* config/riscv/pic.md (*local_pic_load_s<mode>)
 	(*local_pic_load_u<mode>): Explicitly specify the mode iterator
 	referenced by <mode>, giving...

gcc/doc/install.texi

@@ -2535,6 +2535,7 @@ Removes any @option{-O}-started option from @code{BOOT_CFLAGS}, and adds
 @samp{BOOT_CFLAGS='-g -O1'}.
 
 @item @samp{bootstrap-O3}
+@itemx @samp{bootstrap-Og}
 Analogous to @code{bootstrap-O1}.
 
 @item @samp{bootstrap-lto}