bootloader & kernel: Build zlib with -Wno-error=missing-prototypes.

Will be needed for some newer zlib versions.

src/system/boot/libs/Jamfile

@@ -44,6 +44,8 @@ local libFDTSources =
 	fdt_overlay.c
 	;
 
+SubDirCcFlags -Wno-error=missing-prototypes ;
+
 local platform ;
 for platform in [ MultiBootSubDirSetup ] {
 	on $(platform) {

src/system/kernel/lib/zlib/Jamfile

@@ -4,6 +4,8 @@ local zlibSourceDirectory = [ BuildFeatureAttribute zlib : sources : path ] ;
 UseHeaders $(zlibSourceDirectory) ;
 UseHeaders $(zlibSourceDirectory) : true ;
 
+SubDirCcFlags -Wno-error=missing-prototypes ;
+
 local zlibSources =
 	adler32.c
 	crc32.c