justinquinn I have figured out the preliminary cause of the problem. If the ISSM source code is downloaded via git clone git@github.com:ISSMteam/ISSM.git, the above problem would have occurred when I installed triangle. If the ISSM source code is downloaded manually by clicking "Download ZIP", it would have been fine when I installed triangle, as shown the figure below, and the installation feedback is as follows. Although I figured out that different ways to download the source code lead to the success/failure of triangle installation, I do not know the deeper reasons, I hope you can give a solution, thank you!
# ./install-win-msys2-mingw.sh
Archive: triangle.zip
inflating: src/A.poly
inflating: src/README
inflating: src/makefile
inflating: src/showme.c
inflating: src/triangle.c
inflating: src/triangle.h
inflating: src/tricall.c
patching file src/triangle.c
patching file src/triangle.h
patching file src/triangle.h
Hunk #1 succeeded at 253 (offset -6 lines).
gcc -DNO_TIMER -fpic -DTRILIBRARY -shared -o libtriangle.dll triangle.c
triangle.c: In function 'printtriangle':
triangle.c:3681:50: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
3681 | printf("triangle x%lx with orientation %d:\n", (unsigned long) t->tri,
| ^
triangle.c:3687:36: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
3687 | printf(" [0] = x%lx %d\n", (unsigned long) printtri.tri,
| ^
triangle.c:3694:36: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
3694 | printf(" [1] = x%lx %d\n", (unsigned long) printtri.tri,
| ^
triangle.c:3701:36: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
3701 | printf(" [2] = x%lx %d\n", (unsigned long) printtri.tri,
| ^
triangle.c:3710:37: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
3710 | (t->orient + 1) % 3 + 3, (unsigned long) printvertex,
| ^
triangle.c:3717:37: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
3717 | (t->orient + 2) % 3 + 3, (unsigned long) printvertex,
| ^
triangle.c:3724:27: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
3724 | t->orient + 3, (unsigned long) printvertex,
| ^
triangle.c:3730:38: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
3730 | printf(" [6] = x%lx %d\n", (unsigned long) printsh.ss,
| ^
triangle.c:3735:38: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
3735 | printf(" [7] = x%lx %d\n", (unsigned long) printsh.ss,
| ^
triangle.c:3740:38: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
3740 | printf(" [8] = x%lx %d\n", (unsigned long) printsh.ss,
| ^
triangle.c: In function 'printsubseg':
triangle.c:3776:10: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
3776 | (unsigned long) s->ss, s->ssorient, mark(*s));
| ^
triangle.c:3781:36: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
3781 | printf(" [0] = x%lx %d\n", (unsigned long) printsh.ss,
| ^
triangle.c:3788:36: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
3788 | printf(" [1] = x%lx %d\n", (unsigned long) printsh.ss,
| ^
triangle.c:3797:29: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
3797 | 2 + s->ssorient, (unsigned long) printvertex,
| ^
triangle.c:3804:29: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
3804 | 3 - s->ssorient, (unsigned long) printvertex,
| ^
triangle.c:3811:36: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
3811 | printf(" [6] = x%lx %d\n", (unsigned long) printtri.tri,
| ^
triangle.c:3818:36: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
3818 | printf(" [7] = x%lx %d\n", (unsigned long) printtri.tri,
| ^
triangle.c:3827:29: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
3827 | 4 + s->ssorient, (unsigned long) printvertex,
| ^
triangle.c:3834:29: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
3834 | 5 - s->ssorient, (unsigned long) printvertex,
| ^
