cherrypicked typos, errors and clarifications from the documentation-… #4518

Job	Run time
gcc	3m 27s
gcc (--disable-shared)	3m 30s
gcc (--enable-symbols)	3m 21s
gcc (--enable-symbols=mem)	4m 4s
gcc (--enable-symbols=all)	4m 16s
gcc (CFLAGS=-ftrapv)	3m 28s
gcc (CFLAGS=-DTCL_UTF_MAX=4)	3m 30s
gcc (CFLAGS=-DTCL_UTF_MAX=6)	3m 48s
gcc (CFLAGS=-m32 CPPFLAGS=-m32 LDFLAGS=-m32 --disable-64bit)	3m 46s
	33m 10s

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