Linux: improve tryRead macro safety

Add an explicit else clause so a following else branch for a prior if
condition does not get mixed up.

Also force a trailing semicolon and thereby silence current
-Wextra-semi-stmt warnings.

Improve readability of the hwloc_bitmap_foreach_begin loop macro.

configure.ac

@@ -668,6 +668,7 @@ AS_VAR_IF(CACHEVAR,yes,
 AS_VAR_POPDEF([CACHEVAR])dnl
 ])dnl AX_CHECK_COMPILE_FLAGS
 
+AX_CHECK_COMPILE_FLAG([-Wextra-semi-stmt],         [AM_CFLAGS="$AM_CFLAGS -Wextra-semi-stmt"],         , [-Werror=unknown-warning-option]) dnl the autoconf check itself generates -Wextra-semi-stmt
 AX_CHECK_COMPILE_FLAG([-Wimplicit-int-conversion], [AM_CFLAGS="$AM_CFLAGS -Wimplicit-int-conversion"], , [-Werror])
 AX_CHECK_COMPILE_FLAG([-Wnull-dereference],        [AM_CFLAGS="$AM_CFLAGS -Wnull-dereference"],        , [-Werror])
 

linux/LinuxProcessList.c

@@ -1609,7 +1609,7 @@ static inline void LinuxProcessList_scanMemoryInfo(ProcessList* this) {
                (variable) = parsed_;                                         \
             }                                                                \
             break;                                                           \
-         }
+         } else (void) 0 /* Require a ";" after the macro use. */
 
       switch (buffer[0]) {
       case 'M':
@@ -1785,12 +1785,12 @@ static inline void LinuxProcessList_scanZfsArcstats(LinuxProcessList* lpl) {
          if (String_startsWith(buffer, label)) {                               \
             sscanf(buffer + strlen(label), " %*2u %32llu", variable);          \
             break;                                                             \
-         }
+         } else (void) 0 /* Require a ";" after the macro use. */
       #define tryReadFlag(label, variable, flag)                               \
          if (String_startsWith(buffer, label)) {                               \
             (flag) = sscanf(buffer + strlen(label), " %*2u %32llu", variable); \
             break;                                                             \
-         }
+         } else (void) 0 /* Require a ";" after the macro use. */
 
       switch (buffer[0]) {
       case 'c':