Various fixes for building with GCC 10.

Taken from Debian:
https://sources.debian.org/patches/jfsutils/1.1.15-5/gcc10_fix-1.patch/

--- jfsutils-1.1.15.old/fscklog/display.c	2005-11-22 21:43:54.000000000 +0100
+++ jfsutils-1.1.15.new/fscklog/display.c	2020-05-21 18:15:13.410617620 +0200
@@ -54,7 +54,7 @@
  * output: fsck extracted service log I/O buffer
  *
  */
-char xchklog_buffer[XCHKLOG_BUFSIZE];
+static char xchklog_buffer[XCHKLOG_BUFSIZE];
 
 /* + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
  *
diff -ur --exclude '*.o' --exclude '*.a' jfsutils-1.1.15.old/libfs/logredo.c jfsutils-1.1.15.new/libfs/logredo.c
--- jfsutils-1.1.15.old/libfs/logredo.c	2005-11-22 21:43:55.000000000 +0100
+++ jfsutils-1.1.15.new/libfs/logredo.c	2020-05-21 18:19:44.927703271 +0200
@@ -87,9 +87,9 @@
  *    S T U F F    F O R    T H E    L O G
  *
  */
-struct logsuper logsup;		/* log super block */
-int32_t numdoblk;		/* number of do blocks used     */
-int32_t numnodofile;		/* number of nodo file blocks used  */
+static struct logsuper logsup;		/* log super block */
+static int32_t numdoblk;		/* number of do blocks used     */
+static int32_t numnodofile;		/* number of nodo file blocks used  */
 int32_t numExtDtPg = 0;		/* number of extended dtpage blocks used  */
 
 /*
@@ -129,7 +129,7 @@
  */
 
 /* buffer header table */
-struct bufhdr {
+static struct bufhdr {
 	int16_t next;		/* 2: next on free/lru list */
 	int16_t prev;		/* 2: previous on free/lru list */
 	int16_t hnext;		/* 2: next on hash chain */
@@ -142,7 +142,7 @@
 } bufhdr[NBUFPOOL];		/* (24) */
 
 /* buffer table */
-struct bufpool {
+static struct bufpool {
 	char bytes[PSIZE];
 } buffer[NBUFPOOL - 1];
 
@@ -151,15 +151,16 @@
  *
  * log has its own 4 page buffer pool.
  */
-uint8_t afterdata[LOGPSIZE * 2];	/* buffer to read in redopage data */
+static uint8_t afterdata[LOGPSIZE * 2];	/* buffer to read in redopage data */
 
 /*
  * Miscellaneous
  */
-caddr_t prog;			/* Program name */
-int32_t mntcnt, bufsize;
-char *mntinfo;
-int32_t retcode;		/* return code from logredo    */
+static caddr_t prog;			/* Program name */
+extern int32_t mntcnt;
+static int32_t bufsize;
+static char *mntinfo;
+static int32_t retcode;		/* return code from logredo    */
 int end_of_transaction = 0;
 
 /*
cm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/tests/import-utils.scm?id=07ce23e011d18460e7ff5553d4ff640f7073075b&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2019-12-11 12:13:03 +0100'>2019-12-11</span></td><td><a href='/guix/commit/tests/import-utils.scm?id=70a8e13277d4a44b89dd9ee2290b98105f0235f1'>import: utils: 'recursive-import' returns a list rather than a stream.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-12-11 12:12:58 +0100'>2019-12-11</span></td><td><a href='/guix/commit/tests/import-utils.scm?id=ddd59159004ca73c9449a27945116ff5069c3743'>import: utils: 'recursive-import' returns packages in topological order.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-07-25 00:16:41 +0200'>2019-07-25</span></td><td><a href='/guix/commit/tests/import-utils.scm?id=81c3dc32244a17241d74eea9fa265edfcb326f6d'>maint: Switch to Guile-JSON 3.x.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>