Sanitizer warnings

[Algunenano]

While investigating #4381 I've come up with a bunch of warnings from using different sanitizers from the ones we have already setup in Travis.

There are both memory issues (mostly false positives) as implicit integer conversions that might mean a change in value.

WIP in ​https://github.com/postgis/postgis/pull/395 but I might push commits individually for clarity and only backport those where I'm positive it can be an issue.

[algunenano]

In 17411:

Fix several issues when building cunit tests

• loader cunit: Add missing $(CFLAGS) to the main binary
• liblwgeom cunit: Avoid link issues with some sanitizers

References #4383

[algunenano]

In 17412:

lwout_wkb.c: Address implicit type conversion with value change

lwout_wkb.c:288:16: runtime error: implicit conversion from type 'char' of value -16 (8-bit, signed) to type 'uint8_t' (aka 'unsigned char') changed the value to 240 (8-bit, unsigned)
lwout_wkb.c:654:27: runtime error: implicit conversion from type 'uint32_t' (aka 'unsigned int') of value 2147483663 (32-bit, unsigned) to type 'int' changed the value to -2147483633 (32-bit, signed)
lwout_wkb.c:213:16: runtime error: implicit conversion from type 'char' of value -128 (8-bit, signed) to type 'uint8_t' (aka 'unsigned char') changed the value to 128 (8-bit, unsigned)
lwout_wkb.c:607:27: runtime error: implicit conversion from type 'uint32_t' (aka 'unsigned int') of value 2147483651 (32-bit, unsigned) to type 'int' changed the value to -2147483645 (32-bit, signed)

References #4383

[algunenano]

In 17413:

lwout_twkb.c: Address implicit type conversion with value change

lwout_twkb.c:170:9: runtime error: implicit conversion from type 'long long' of value 10000000000 (64-bit, signed) to type 'int' changed the value to 1410065408 (32-bit, signed)

References #4383

[algunenano]

In 17414:

Multiple fixes for undefined behaviour in implicit conversions

shp2pgsql-core.c:839:22: runtime error: implicit conversion from type 'int' of value -1 (32-bit, signed) to type 'DBFFieldType' changed the value to 4294967295 (32-bit, unsigned)

runtime error: implicit conversion from type 'int32' (aka 'int') of value -1 (32-bit, signed) to type 'uint32' (aka 'unsigned int') changed the value to 4294967295 (32-bit, unsigned)
UndefinedBehaviorSanitizer: undefined-behavior lwgeom_functions_basic.c:2237:10 in

runtime error: implicit conversion from type 'unsigned int' of value 4294967295 (32-bit, unsigned) to type 'int' changed the value to -1 (32-bit, signed)
UndefinedBehaviorSanitizer: undefined-behavior ptarray.c:333:13 in

runtime error: implicit conversion from type 'unsigned int' of value 4294967295 (32-bit, unsigned) to type 'int' changed the value to -1 (32-bit, signed)
UndefinedBehaviorSanitizer: undefined-behavior ptarray.c:333:13 in

References #4383

[algunenano]

In 17480:

Fix undefined behaviour in implicit conversions

Cleans up errors in raster and topology and adds an
extra sanitizer build in Travis

Closes #4383
Closes ​https://github.com/postgis/postgis/pull/398