build: macOS configure fails to find gmp installed by brew

[PastaPastaPasta]

On macOS, when compiling without depends, I get this output from configure

checking if evhttp_connection_get_peer expects const char**... no
checking for libqrencode... yes
checking for libzmq >= 4... yes
CPPFLAGS =  -DHAVE_BUILD_INFO -DGSL_NO_IOSTREAMS -I/opt/homebrew/opt/gmp/include -I/opt/homebrew/opt/miniupnpc/include -I/opt/homebrew/opt/libnatpmp/include -DMAC_OSX -DOBJC_OLD_DISPATCH_PROTOTYPES=0 -DPROVIDE_FUZZ_MAIN_FUNCTION
checking for gmp.h... no
configure: error: libgmp headers missing

However if I first:

export CPPFLAGS="-I/opt/homebrew/opt/gmp/include"
export LDFLAGS="-L/opt/homebrew/opt/gmp/lib"

Then configure works as expected, and I am able to compile