trying to build gcc-10.2 I've added the latest sources for the GMP, MPFR, MPC, ISL libraries My system is CentOS 7.8 with gcc version 4.85 I'm running configure with the following parameters: CC=/usr/bin/gcc CXX=/usr/bin/g++ ../gcc-10.2.0/configure CFLAGS="-std=gnu99" CXXFLAGS="-std=c++11" --prefix=$HOME/.local/gcc-10 --disable-multilib the additional CFLAGS and CXXFLAGS parameters where added to try to fix the error (below) when I run make, I get the error: libtool: compile: /usr/bin/gcc -DHAVE_CONFIG_H -I. -I../../../gcc-10.2.0/gmp/mpn -I.. -D__GMP_WITHIN_GMP -I../../../gcc-10.2.0/gmp -DOPERATION_compute_powtab -DNO_ASM -g -c compute_powtab.c -o compute_powtab.o compute_powtab.c: In function 'mpn_compute_powtab_mul': compute_powtab.c:142:3: error: 'for' loop initial declarations are only allowed in C99 mode for (long pi = start_idx; pi >= 0; pi--) ^ compute_powtab.c:142:3: note: use option -std=c99 or -std=gnu99 to compile your code compute_powtab.c: In function 'mpn_compute_powtab_div': compute_powtab.c:226:3: error: 'for' loop initial declarations are only allowed in C99 mode for (long pi = n_pows - 1; pi >= 0; pi--) ^ compute_powtab.c:274:13: error: redefinition of 'pi' for (long pi = n_pows; pi >= 0; pi--) ^ compute_powtab.c:226:13: note: previous definition of 'pi' was here for (long pi = n_pows - 1; pi >= 0; pi--) ^ compute_powtab.c:274:3: error: 'for' loop initial declarations are only allowed in C99 mode for (long pi = n_pows; pi >= 0; pi--) ^ compute_powtab.c: In function 'powtab_decide': compute_powtab.c:296:3: error: 'for' loop initial declarations are only allowed in C99 mode for (size_t pn = (un + 1) >> 1; pn != 1; pn = (pn + 1) >> 1) ^ compute_powtab.c:304:10: error: redefinition of 'pn' size_t pn = un - 1; ^ compute_powtab.c:296:15: note: previous definition of 'pn' was here for (size_t pn = (un + 1) >> 1; pn != 1; pn = (pn + 1) >> 1) ^ compute_powtab.c:308:3: error: 'for' loop initial declarations are only allowed in C99 mode for (long i = n_pows - 2; i >= 0; i--) ^ make[5]: *** [compute_powtab.lo] Error 1 what flags should I specify to fix this error?