Fix `clang` compilation errors and warnings

[dvorka]

Compiler log:

➜  hstr git:(dev-3.2.0) make clean all
rm -f hashset.o hstr_blacklist.o hstr_curses.o hstr_favorites.o hstr_history.o hstr_regexp.o hstr_utils.o hstr.o radixsort.o main.o
rm -f *~ core *.core
ccache gcc -c -pipe -O2  -arch x86_64 -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX12.1.sdk -mmacosx-version-min=10.10 -Wall -W -fPIC -DDEBUG_NO_TIOCSTI -I. -I../../../../Qt/5.9.9/clang_64/mkspecs/macx-clang -o hashset.o src/hashset.c
ccache gcc -c -pipe -O2  -arch x86_64 -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX12.1.sdk -mmacosx-version-min=10.10 -Wall -W -fPIC -DDEBUG_NO_TIOCSTI -I. -I../../../../Qt/5.9.9/clang_64/mkspecs/macx-clang -o hstr_blacklist.o src/hstr_blacklist.c
ccache gcc -c -pipe -O2  -arch x86_64 -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX12.1.sdk -mmacosx-version-min=10.10 -Wall -W -fPIC -DDEBUG_NO_TIOCSTI -I. -I../../../../Qt/5.9.9/clang_64/mkspecs/macx-clang -o hstr_curses.o src/hstr_curses.c
ccache gcc -c -pipe -O2  -arch x86_64 -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX12.1.sdk -mmacosx-version-min=10.10 -Wall -W -fPIC -DDEBUG_NO_TIOCSTI -I. -I../../../../Qt/5.9.9/clang_64/mkspecs/macx-clang -o hstr_favorites.o src/hstr_favorites.c
ccache gcc -c -pipe -O2  -arch x86_64 -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX12.1.sdk -mmacosx-version-min=10.10 -Wall -W -fPIC -DDEBUG_NO_TIOCSTI -I. -I../../../../Qt/5.9.9/clang_64/mkspecs/macx-clang -o hstr_history.o src/hstr_history.c
src/hstr_history.c:175:52: error: no member named 'size' in 'HISTORY_STATE'
        unsigned radixMaxKeyEstimate=historyState->size*1000;
                                     ~~~~~~~~~~~~  ^
src/hstr_history.c:181:34: error: implicit declaration of function 'history_list' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
        HIST_ENTRY **historyList=history_list();
                                 ^
src/hstr_history.c:181:34: note: did you mean 'history_get'?
/Library/Developer/CommandLineTools/SDKs/MacOSX12.1.sdk/usr/include/readline/history.h:153:13: note: 'history_get' declared here
HIST_ENTRY      *history_get(int);
                 ^
src/hstr_history.c:181:22: warning: incompatible integer to pointer conversion initializing 'HIST_ENTRY **' (aka 'struct _hist_entry **') with an expression of type 'int' [-Wint-conversion]
        HIST_ENTRY **historyList=history_list();
                     ^           ~~~~~~~~~~~~~~
src/hstr_history.c:197:37: warning: passing 'const char *' to parameter of type 'char *' discards qualifiers [-Wincompatible-pointer-types-discards-qualifiers]
            line=parse_history_line(historyList[i]->line);
                                    ^~~~~~~~~~~~~~~~~~~~
src/hstr_history.c:102:32: note: passing argument to parameter 'l' here
char* parse_history_line(char *l)
                               ^
src/hstr_history.c:318:25: error: no member named 'entries' in 'HISTORY_STATE'
        l=historyState->entries[offset]->line;
          ~~~~~~~~~~~~  ^
src/hstr_history.c:325:16: error: implicit declaration of function 'free_history_entry' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
               free_history_entry(remove_history(offset));
               ^
src/hstr_history.c:325:16: note: did you mean 'replace_history_entry'?
/Library/Developer/CommandLineTools/SDKs/MacOSX12.1.sdk/usr/include/readline/history.h:155:13: note: 'replace_history_entry' declared here
HIST_ENTRY      *replace_history_entry(int, const char *, histdata_t);
                 ^
src/hstr_history.c:327:36: error: no member named 'entries' in 'HISTORY_STATE'
                   l=historyState->entries[offset-1]->line;
                     ~~~~~~~~~~~~  ^
src/hstr_history.c:358:83: error: no member named 'entries' in 'HISTORY_STATE'
            fprintf(stdout, "Deleting command '%s' from history\n", historyState->entries[historyState->length-2]->line);
                                                                    ~~~~~~~~~~~~  ^
src/hstr_history.c:360:9: error: implicit declaration of function 'free_history_entry' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
        free_history_entry(remove_history(historyState->length-1));
        ^
2 warnings and 7 errors generated.
make: *** [hstr_history.o] Error 1