Conditionalize the bzip2/gzip compression/decompression

code on the existence of the relevant libraries (actually,
the existence of the include files).

This will allow the library to be easily ported to systems
that don't have these libraries.  (Of course, it also means
that clients using the library on such systems will not be
able to take advantage of the automatic compression format
detection.)

lib/libarchive/archive_read_support_compression_all.c

@@ -32,8 +32,13 @@ __FBSDID("$FreeBSD$");
 int
 archive_read_support_compression_all(struct archive *a)
 {
+#if HAVE_BZLIB_H
 	archive_read_support_compression_bzip2(a);
+#endif
+	/* The decompress code doesn't use an outside library. */
 	archive_read_support_compression_compress(a);
+#if HAVE_ZLIB_H
 	archive_read_support_compression_gzip(a);
+#endif
 	return (ARCHIVE_OK);
 }

lib/libarchive/archive_read_support_compression_bzip2.c

@@ -25,6 +25,10 @@
  */
 
 #include "archive_platform.h"
+
+/* Don't compile this if we don't have bzlib. */
+#if HAVE_BZLIB_H
+
 __FBSDID("$FreeBSD$");
 
 #include <err.h>
@@ -361,3 +365,5 @@ drive_decompressor(struct archive *a, struct private_data *state)
 	    a->compression_name);
 	return (ARCHIVE_FATAL);
 }
+
+#endif /* HAVE_BZLIB_H */

lib/libarchive/archive_read_support_compression_gzip.c

@@ -25,6 +25,10 @@
  */
 
 #include "archive_platform.h"
+
+/* Don't compile this if we don't have zlib. */
+#if HAVE_ZLIB_H
+
 __FBSDID("$FreeBSD$");
 
 #include <errno.h>
@@ -496,3 +500,5 @@ drive_decompressor(struct archive *a, struct private_data *state)
 	    a->compression_name);
 	return (ARCHIVE_FATAL);
 }
+
+#endif /* HAVE_ZLIB_H */

lib/libarchive/archive_write_set_compression_bzip2.c

@@ -25,6 +25,10 @@
  */
 
 #include "archive_platform.h"
+
+/* Don't compile this if we don't have bzlib. */
+#if HAVE_BZLIB_H
+
 __FBSDID("$FreeBSD$");
 
 #include <errno.h>
@@ -326,3 +330,5 @@ drive_compressor(struct archive *a, struct private_data *state, int finishing)
 		}
 	}
 }
+
+#endif /* HAVE_BZLIB_H */

lib/libarchive/archive_write_set_compression_gzip.c

@@ -25,6 +25,10 @@
  */
 
 #include "archive_platform.h"
+
+/* Don't compile this if we don't have zlib. */
+#if HAVE_ZLIB_H
+
 __FBSDID("$FreeBSD$");
 
 #include <errno.h>
@@ -381,3 +385,5 @@ drive_compressor(struct archive *a, struct private_data *state, int finishing)
 		}
 	}
 }
+
+#endif /* HAVE_ZLIB_H */