Install gensim fails because C code is not ANSI-compliant

[hstk30]

Problem description

Can't use pip install gensim to install the latest gensim

Steps/code/corpus to reproduce

building 'gensim.similarities.fastss' extension
    creating build/temp.linux-x86_64-3.6/gensim/similarities
    gcc -pthread -Wno-unused-result -Wsign-compare -DNDEBUG -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switch$s -m64 -mtune=generic -D_GNU_SOURCE -fPIC -fwrapv -fPIC -I/nas/home/hstk/gitProject/venv/centaur/include -I/usr/include/python3.6m -I/nas/home/hstk/gitProject/venv/centaur/lib64/pyth$n3.6/site-packages/numpy/core/include -c gensim/similarities/fastss.c -o build/temp.linux-x86_64-3.6/gensim/similarities/fastss.o
    gensim/similarities/fastss.c: 在函数‘ceditdist’中:
    gensim/similarities/fastss.c:725:9: 错误：只允许在 C99 模式下使用‘for’循环初始化声明
             for (WIDTH tmpi = 0; tmpi <= len_s1; tmpi++) row2[tmpi] = tmpi;
             ^
    gensim/similarities/fastss.c:725:9: 附注：使用 -std=c99 或 -std=gnu99 来编译您的代码
    gensim/similarities/fastss.c:727:9: 错误：只允许在 C99 模式下使用‘for’循环初始化声明
             for (WIDTH i2 = 0; i2 < len_s2; i2++) {
             ^
    gensim/similarities/fastss.c:738:13: 错误：只允许在 C99 模式下使用‘for’循环初始化声明
                 for (WIDTH i1 = 0; i1 < len_s1; i1++) {
                 ^
    error: command 'gcc' failed with exit status 1

Sorry, the error info have Chinese, but I think It's easy to figure out the error.

Now, I try to install gensim==4.0.0, it's OK.

Versions

Linux-3.10.0-1127.18.2.el7.x86_64-x86_64-with-centos-7.8.2003-Core
Python 3.6.8 (default, Apr  2 2020, 13:34:55)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-39)]
Bits 64
NumPy 1.19.5
SciPy 1.5.4

[piskvorky]

What's the error? Are you able to submit a PR with a fix?