Add more warnings and reenable -Werror.

These find an old bug-let in hts_parse_format():
The buffer size is 8, but it includes \0 so the string would have been
truncated, causing the strcmp to fail for "fastq.gz".

Curiously gcc 10 and 11 spot this, but not gcc 12 or 13, nor clang.

Some builds didn't have -Werror enabled, such as those without
./configure and on Windows.

.cirrus.yml

@@ -72,6 +72,7 @@ gcc_task:
        DO_MAINTAINER_CHECKS: yes
        DO_UNTRACKED_FILE_CHECK: yes
        USE_CONFIG: no
+       CFLAGS: -g -O2 -Wall -Werror -fvisibility=hidden
     - environment:
        USE_CONFIG: yes
        # ubsan is incompatible with some -Wformat opts so we do that on clang.
@@ -141,7 +142,7 @@ rocky_task:
     LC_ALL: C
     CIRRUS_CLONE_DEPTH: 1
     USE_CONFIG: yes
-    CFLAGS: -std=gnu90 -Wformat -Wformat=2
+    CFLAGS: -g -O3 -std=gnu90 -Wformat -Wformat=2 -Wextra -Wno-sign-compare -Wno-unused-parameter -Wno-missing-field-initializers -Wno-empty-body
 
   # NB: we could consider building a docker image with these
   # preinstalled and specifying that instead, to speed up testing.

.github/workflows/windows-build.yml

@@ -29,7 +29,7 @@ jobs:
         export PATH="/mingw64/bin:$PATH:/c/Program Files/Git/bin"
         export MSYSTEM=MINGW64
         autoreconf -i
-        ./configure
+        ./configure --enable-werror
         make cc-version
         make -j6
     - name: Check Htslib

hts.c

@@ -1322,7 +1322,7 @@ int hts_parse_opt_list(htsFormat *fmt, const char *str) {
  *        -1 on failure.
  */
 int hts_parse_format(htsFormat *format, const char *str) {
-    char fmt[8];
+    char fmt[9];
     const char *cp = scan_keyword(str, ',', fmt, sizeof fmt);
 
     format->version.minor = 0; // unknown

test/test-bcf-sr.c

@@ -179,6 +179,7 @@ int main(int argc, char *argv[])
                 break;
             case 'h':
                 usage(EXIT_SUCCESS);
+                // fall-through
             default: usage(EXIT_FAILURE);
         }
     }