Oh boy, neither GCC nor Clang liked the Unicode one bit:
$ make 2>&1 | head
c++ -std=c++17 -Wall -Wextra -Os -MD -MP -MF cxxmatrix.dep -c -o cxxmatrix.o cxxmatrix.cpp
In file included from cxxmatrix.cpp:595:
glyph.inl:78:2: error: converting to execution character set: Invalid argument
78 | {U'�', 21, {127, 65, 65, 65, 65, 65, 127, }},
| ^~~~
glyph.inl:79:2: error: converting to execution character set: Invalid argument
79 | {U'�', 21, {573695, 2072768, 104616, 104344, 37000, 1609860, 430211, }},
| ^~~~
glyph.inl:80:2: error: converting to execution character set: Invalid argument
80 | {U'�', 21, {164354, 260859, 2015779, 1221155, 692770, 429602, 1238014, }},
