brew: autodetect path when building formulas

When `brew install` builds from source, the brew binary
is not necessarily in PATH, so autodetect it in a way
that works for both intel and arm.

Ref dciabrin/homebrew-ngdevkit#4

Makefile

@@ -88,7 +88,8 @@ GDB_LD_BUILD_FLAGS=
 GDB_PKG_CONFIG_PATH=
 
 ifeq ($(shell uname -s),Darwin)
-HOMEBREW_PREFIX=$(shell brew --prefix)
+HOMEBREW_PREFIX=$(shell PATH="$$PATH:/opt/homebrew/bin:/usr/local/bin" brew --prefix)
+
 GDB_C_BUILD_FLAGS+=-I$(HOMEBREW_PREFIX)/opt/readline/include
 GDB_CXX_BUILD_FLAGS+=-I$(HOMEBREW_PREFIX)/opt/readline/include
 GDB_LD_BUILD_FLAGS+=-L$(HOMEBREW_PREFIX)/opt/readline/lib